Ford Mustang Forums banner

1 - 10 of 10 Posts

738 Posts
Discussion Starter #1
I'm about to undergo a converion from what used to be a 4 cylinder mustang to an EFI 5 litre setup. It has been converted to v8 already, but it's carb'd. I like to be able to start my car below freezing with no problems.. If anyone has performed this before and could tell what I need, please help. Any links would be appreciated as well, thanks.


3,694 Posts
Here's a good writeup on a carb to efi swap...

I'm converting my '85 GT to EFI and found this during my research. Author unknown...

This isn't Mustang specific but there is some good info in it.

USED parts

Upper and lower intake manifolds from 5.0 fuel injected engine. Ensure they are complete with all sensors, injectors , fuel rails and injector wiring harness harnesses.

O2 sensor harness

Main wiring harness including fuel pump relay and EEC relay ( available new from various sources)

Distributor ( Roller Cam engines use steel distributor gears that will eat the softer cast cam gear on the 302 cam so it will have to be changed)

Coil from Donor vehicle

Computer from Donor Vechicle

Throttle cable (mustang cables work)

New Parts

High Pressure fuel pump ( 40 to 50 PSI) (86' F250 external 5.0L pump or Thunderbird)

Air Filter system (K&N air filter RU-3130 7" conical)

02 sensors to match the year of the harness you are using.

O2 sensor bungs


Bronze or cast iron distributor gear


Low pressure high volume fuel pump

Wild Child accumulator tank




Remove the air cleaner, choke cable, throttle linkage, and transmission kickdown linkage. Remove intake manifold and carburator. You may want to remove any accessories such as windshield washer reservoir, pump, or existing emissions control hardware on the fender aprons.


Label all electrical wires as they are released. Disconnect the battery cables, temperature guage sender, oil pressure sender, choke heater (if equipped), neutral start switch, coil power supply, and starter cable to solenoid. Remove coil and Distributor.



Install lower manifold, New Distributor ( with new softer drive gear) decide on location for solenoids, relays, computer.

Run wiring

Mount Throttle cable

Install upper manifold


Since the existing system is low pressure, ALL rubber fuel lines between the new high pressure fuel pump and the fuel rails must be replaced with high pressure fuel injection hose with high pressure clamps The high pressure fuel line clamps don’t have the slots for the worm in the hose band and can be tightened further than normal hose clamps.

Drain the fuel system. The easiest way is to disconnect and remove the rubber hose directly under the tank. The fuel system will empty quickly so be prepared with several small fuel cans.

Disconnect the fuel supply line from the engine. Remove the rubber line that connects the suction line to the pump.

Disconnect the wiring and the fuel line to the fuel sender unit. Remove the sender from the tank and allow all residual gasoline to evaporate from the sender unit before modifying the unit for a fuel return line.

Vacuum System

The center of the upper intake on the SEFI engine will have one large fitting with two smaller connections that face the firewall and a single large fitting that faces the front of the engine. The large fitting that faces the firewall normally connects to the vacuum tree and supplies the power brake booster. The MAP sensor is usually connected to the vacuum tree also( Speed density systems only). The two smaller fittings are connected to the fuel pressure regulator and to the line that supplies the EVP, TAD, and TAB solenoids. ( Most people mount the TAB and TAD solenoids with no vacuum. This shows the computer they are mounted, but makes them ineffective. Others have found no problems running without them at all, it has been rumored that the computer will not go into "closed loop mode" without them connected)The single large fitting facing forward connects to the charcoal canister purge valve. If your vehicle is not equipped with a charcoal canister, then this line needs to have a small breather filter attached beyond the canister purge solenoid. The injectors and Idle Air Bypass Valve are calibrated for the additional air coming in from the canister purge( This information not confirmed). An orifice may be required in the canister purge line to control air flow if the canister is not used.

Throttle Cable

Install mustang throttle cable

Air Cleaner

A round K&N air cleaner makes a simple install. Some people have been successful installing the stock air box.

Exhaust System

You can chose to use the cast iron exhaust manifolds from a Crown Victoria because had the O2 sensors are mounted in the top of the manifolds while the Mustang headers are more bulky and , O2 sensor bosses must be welded into the existing down pipes.


High Pressure Requirements

The existing fuel system is a low pressure (~4psi) system. SEFI requires a 40 psi differential pressure across the fuel injectors so some modifications need to be made. Since the system is low pressure, ALL rubber fuel lines must be replaced with high pressure fuel injection hose with high pressure clamps The high pressure fuel line clamps don’t have the slots for the worm in the hose band and can be tightened further than normal hose clamps. ( Optional The wild child accumulator tank, or something similar can be used to ensure that you don't run out of fuel going up hill. Stock Bronco tanks don't have baffles necessary to hold fuel for these instances check out

Fuel Pump Selection

I experimented with modifying the in cab tank sender unit to hold an in-tank pump, but finally settled on a dual pump arrangement. The in-line Thunderbird high pressure pump has no suction capability and cannot pull fuel up the fuel pickup tube. (Optional) A small universal low pressure electric fuel pump is needed to ensure that the in-line pump always has fuel available. The in-line pump has a capacity of approximately 88 liters/hr and the low pressure pump has a capacity of 110 liters/hr. With a stock Speed Density setup, I haven’t seen any problems with fuel system capacity.

Fuel Return Line

Because a SEFI engine has a fuel pressure regulator that maintains pressure by dumping fuel back into the tank, the fuel system MUST have a return line. This means that an additional line must be run back to the fuel tank. I modified the fuel sender unit so that it contained a fuel return line by drilling a 5/16" hole through the sender flange housing and then soldering a 5/16" tube in place. Anyone who has sweated a few plumbing fittings won’t have a problem doing this. I also put one of the rubber nipples on the return line that are commonly seen on fuel injection pump assemblies to make sure the return fuel doesn’t create foam inside the tank. Another approach is to put a "T" into the vent tube for the fuel tank, and run the return there.[New 7/16/01, some folks just put a "T" in the line before the high pressure fuel pump and run the fuel return to there., apparently no one has seen problems with this, but it looks like it could lead to over pressurizing the low pressure side if you did it.]

Fuel Pump Connection

I mounted the high pressure pump in the engine bay in order to keep the lenght of high pressure hose required to a minumum. If you do this you must use a high volume pump to supply the high pressure pump since it is not self priming. The low pressure( high volume) pump must be mounted near the fuel tank, and be sure to put filters in front of the pumps. Some people use just the high pressure pumps successfully but they must be mounted near the fuel tanks. The accumulator tank system requires a low pressure pump supply and the high pressure pump.

Connect the engine fuel supply and return lines to the fuel lines run earlier. The forward most line on the engine is the supply. I cut the original supply lines, NOT THE FUEL RAILS, 2-5 inches beyond the spring lock couplers and used fuel injection hose and hose clamps. Fuel injection hose clamps don’t have the slots for the worm in the hose band and can be tightened further than normal hose clamps.



This is probably the part that really keeps most people from doing this conversion. Actually, wiring connections are pretty straight forward. The EEC IV computer harness is pretty much a stand alone system.

To make the computer come alive, only 5 connections need to be made.

To give the computer control of the fuel pump an additional 3 wires need to be hooked up.

For the power hungry, an additional connection is required to allow the computer to turn off AC under WOT.

To route the oil pressure and water temperature guages through the wires supplied in the engine harness, two more connections are required.

The neutral start switch requires two more connections and if desired, cruise control requires two more connections.

In total, perhaps 12 or 13 wires need to be connected, however, when approached from a system point of view, its not overwhelming. Check out Appendixes A, and B, for generic harness connections.

Wiring Identification And Harness Installation

Disconnect and mark all wires that went to the engine and transmission.

The following wires should be identified in the old harness:

Ignition Power To Coil (Resistance wire - CAUTION) Red/Green

Starter Relay To Coil Red/Blue

Temperature Sender Red/White

Oil Pressure Sender White/Red

Neutral Start Switch wires Red/Blue or White/Pink

Backup Light Wires (If So Equipped)

Starter Solenoid wire Red/Blue

I also suggest that you lay out your computer harness across the firewall before installation. The harness can be mounted to the firewall much easier with the engine out. I chose to mount the TAD/TAB solenoids, EGR valve positioner, vacuum accumulator, and the MAP sensor on the right side of the firewall directly above the heater hose connections. The EEC relay, fuel pump relay, inertia switch, and ignition coil were mounted on the left fender apron. I mounted the computer on the left fender apron, however, I have reservations about its reliability in the engine compartment since Ford chose to put all engine computers under the dash.

I ran an additional 10 gage wire from the starter relay parallel to the harness over to the area of the relays to power the O2 sensors and to be the power source for the relays. I put a 20 amp inline fuse in this wire. I also used a generic Bosch relay to supply clean 12 volt power on ignition to the EEC relay. I was concerned that the ignition coil supply was a resistance wire and didn’t want to take a chance on the EEC relay not engaging cleanly. In addition, the O2 sensors need to be powered by a high amperage ignition switched wire.


To start with, the computer harness connects to the starter relay for power and has a ground connection that should be connected to the negative battery terminal. The computer is sensitive to ground integrity so don’t skimp and connect the harness to sheet metal. On a Crown Victoria harness, these connections are exactly where needed. When using a Mustang or Thunderbird computer harness, the battery and solenoid need to be relocated to the drivers side of the truck. In this case, the alternator and solenoid wiring needs to be lengthened also. All of the other connections will be made in the three connectors that are located next to the computer in a Crown Victoria harness. For a Mustang harness, the fuel pump connections are located next to the computer and the other connections are in the two connectors near the master cylinder.

Ford decided that the entire computer system should be powered from a single relay. They called it the EEC power relay. This relay has a black casing and is made into the harness. It has a large gage yellow wire that is directly connected to the battery side of the starter solenoid. It has multiple red wires that then power the computer and various subsystems.

The EEC relay is engaged by supplying 12 volts from the ignition switch in the "ON" position to a red/light green wire located in one of the harness connectors. The r/lg wire can be identified by checking for continuity at the ignition coil connector since it also powers the coil. Be careful not to use the wire which supplied the original coil for either the EEC relay or the O2 sensors since it is a "RESISTANCE" wire. Under load, the wire has enough resistance to reduce voltage to the O2 sensors, ignition coil, and EEC relay to less than 9 volts. Either replace the wire completely or use it to switch another relay for clean, FUSED 12 volt power.

The ignition coil and TFI module also need to be powered while the starter is engaged. Connect the red/blue wire in the harness to the starter solenoid wire. This wire is also connected to the neutral start switch. Refer to the neutral start switch section for more detail.


The power to the heated O2 sensors should come from outside of the EEC relay. The Crown Victoria harness has a gray fuse link to the O2 sensors which needs to be connected to a good 12 volt ignition switched source. The O2 sensors also need to be grounded. The Mustang harness and the Crown Victoria harness grounds the O2 sensors in different ways so they will need to be connected between the harnesses. The Mustang harness grounds both O2 sensors through a single orange wire located in the multi-wire white plug at the rear of the engine. The Crown Victoria harness grounds each O2 sensor individually to the block near the air injection manifold location without going through the multi-wire plug. This sounds complex but it really isn’t. Simply connect the engine O2 ground wire to the two wires in the Crown Victoria O2 sensor harness and then ground them to either the engine or the frame.


The fuel pump is powered by another relay. This relay is controlled by the computer by grounding the relay coil. Normally, the same yellow wire that supplies the EEC relay supplies the fuel pump relay. EEC relay "ENERGIZED" power is supplied by the EEC Power relay through the inertia switch to the relay coil. When the relay is grounded by the computer, the yellow wire is connected to the fuel pump wire. The relay needs to have a switched source of coil power because the computer drops its control back to ground when it powers down. If an ignition switched coil power source is not used then the pump will run continuously. When the system is wired properly, the fuel pump will run for 2 seconds when the ignition is turned on. After 2 seconds, the computer turns the pump off unless it detects rotation of the distributor through the TFI module. Grounding the tan/light green wire on the self test plug should make the pump run if the ignition is "ON".

The inertia safety switch disconnects the power to the relay coil, turning the fuel pump off, in the event of an accident. The inertia switch is wired in the coil relay circuit so that it doesn’t have to handle large current flow.


The engine harness has the wires for both the temperature and oil pressure gage. The wires in the existing truck harness can be connected at the harness connection point by matching wire colors. The temperature gage is red/white and the oil pressure is white/red. The instruments used in a late model Mustang have different ohm resistance than the instruments used in a classic truck. The sending units on the engine will need to be replaced with the ones from the old truck engine in order for the gages to work properly. The instrument wires do NOT need to be connected for the computer to work properly.


The harness to the AOD transmission will have four wires. Two wires are for the neutral start switch and two are for the backup light switch. The neutral start switch needs to be connected to prevent the engine from starting in any gear position except Neutral and Park. The computer wants to know when the transmission is in gear so it also monitors this connection. The computer will operate correctly without being connected to the switch, but, a fault code (#67) will be set.

The trucks existing harness most likely has a red/blue wire that went through the old neutral start switch to the starter solenoid. Connect the ignition switch side of this wire to one of the white/pink wires in the transmission harness and to the red/blue wire in the computer harness (mentioned previously) so that the ignition coil and TFI module are powered during start. Connect the white/pink wire in the computer harness and the other white/pink wire in the transmission harness to the red/blue wire that goes to the solenoid. The computer has to see the resistance of the solenoid coil in order for it to determine gear status.


The computer harness contains the wiring connections to the AC clutch and pressure switch. Connect the green wire (most likely) from the truck harness to the light green/pink wire in the computer harness. The computer harness has a relay that it uses to turn the AC off during WOT. The AC connection does NOT need to be made in order for the computer to work properly.


Some versions of the EEC computers have integrated cruise control. The Mustang does not while 87 up Crown Victoria’s and Thunderbirds do. Mass Air Mustangs use the VSS to control transition to idle as the car stops. Simply connect the wires from the VSS sensor to the dark green/white and black/white wires that connect to pins 3 and 6 on the EEC computer. The VSS sensor does NOT need to be installed to have the computer operate correctly unless you are using a Mass Air system.


I know this is scary, but there will be some wires that are not connected. Depending on the year harness, there may be wires for a brake on/off switch, speed control command switch, vehicle speed control solenoid, and data output link.


Before installing the computer and powering up, there are several quick electrical checkouts that can be done to make sure that major wiring errors don’t exist.

The first check is to make sure that 12 volt power is available to the TFI connector at the correct terminals with the switch in "RUN" and "START".

Disconnect the EEC computer.

Disconnect the connector to the TFI module on the distributor.

Unplug the fuel pump relay

Disconnect the "S" wire at the starter solenoid

Hold the TFI connector so that the terminals face out with the locking tab to the right.

The connector pins are referred to as #1 at the bottom up to #6 at the top.

Insert a straight pin into the terminal being probed.

Use a VOM to check for +12 volts on pins #2 and #3 with the ignition switch in "RUN"

Use a VOM to check for +12 volts on pins #3 and #4 with the ignition switch in "START"

If OK, connect all connectors except EEC and fuel pump

Use a VOM to check for +12 volts on the red/green wire at the ignition coil in "RUN" and "START"

Use a VOM to check for +12 volts on the red wire at the TAD and TAB solenoids, EVR, Canister Purge Solenoid, and at the Idle Speed Air Bypass Valve in the "RUN" position

Turn ignition switch to "OFF"

Disconnect the O2 sensors from the O2 sensor harness.

Turn ignition switch to "RUN"

Use a VOM to check for +12 volts on the gray wire in each harness sensor connector

Turn ignition switch "OFF"

Check that the black/light green wire in each sensor connector has ground continuity

Reconnect the O2 sensors.

Ensure the left O2 sensor connector has the dark blue/light green wire.

Connect the EEC computer and the fuel pump relay.

Verify that all fuel lines are installed and tight.

Turn the ignition switch to "RUN"

Fuel pump should run for 2 seconds

If the fuel pumps don’t run, see the ‘No Start - Fuel System’ section below

Cycle the ignition switch from "OFF" to "RUN" several times to build fuel pressure

Take a deep breath and START THE ENGINE


So it didn’t start? Don’t give up just yet. I hope that you remembered to put fuel back in the tank. We did drain it in an earlier step.

Seriously, several of my conversions didn’t start immediately. After weeding out simple things like wiring errors and defective pumps, I traced the problems to a defective distributor stator in one case and a defective fuel pressure regulator in another case.

What to do if it doesn't start.

1) Does the fuel pump run for 2 seconds after you turn the key to run?

Yes, go onto #2

No, The computer grounds the fuel pump relay to complete the circuit. If you ground the plug on the test connector that connects to the fuel pump the fuel pump should run. If not you have either wired the fuel pump incorrectly or you have a bad fuel pump.

#2) Attach a timing light to the #1 plug wire and crank the engine. Does the light "strobe" as it should?

Yes, Ensure timing is approximately 10BTDC. and go to #3

No, check your coil wiring and perform the tests below.

#3) Remove a spark Plug , does it have fuel on it?

No. Then your fuel injectors probably aren't sending fuel to the cylinders. They are connected to the computer through the black plug located on the upper intake manifold. Disconnect the black connector and check to see that the center electrode, has 12V power with the key on. The outer pins are used to ground each individual injector in order to make them fire. Try making a jumper to connect the make and female center electrode, then one at a time, ( with the key on) ground the individual pins on the lower connector to the negative side of the battery, you should hear a clicking noise. To cure my problem, I used the jumper on the self test port to run the fuel pump while I kept grounding each injector ( just tapping it so not to over heat the windings) after a few minutes it would start clicking. I did this until I had about 5 working injectors, and then I started the engine and let it idle, the others all cleared themselves. Though I added some fuel injector cleaner to the tank to make sure they stayed working.

No Start - Fuel System

The first thing to check for is fuel pressure. There is a Schrader fitting (looks like a tire stem) on the fuel pressure regulator where pressure can be checked. The regulator is just behind the throttle body and should have a vacuum line attached. Remove the protective cap and attach a high pressure gage. Fuel pressure should be approximately 40 psi engine off and 36 psi engine running at idle. If you don’t have a high pressure gage then depress the stem carefully. Fuel should flow freely out of the fitting.

I suggest the following steps to debug a fuel system problem.

Check that both fuel pumps run. If only one pump runs, then the other pump is either defective or incorrectly grounded. If only the high pressure pump runs when the key is turned to run, then fuel is not being primed. Without a low pressure pump, the in-line high pressure pump will NEVER pick up the fuel. If only the low pressure pump runs, then there is not enough fuel pressure to spray fuel through the injectors. If both pumps run, but the fuel pressure is low or nonexistent. check the pickup tube in the tank for holes or obstructions. Also verify that you have the suction side of the low pressure pump connected to the existing pickup tube in the tank.

If the pumps don’t run, then the next step is to determine if the inertia switch, fuel pump relay, or pump wiring is at fault. A quick test is to run a wire directly from the positive terminal on the battery to the fuel pumps. If the pumps don’t run, then the pumps are either defective or incorrectly grounded.

If the pumps run when connected directly to the battery, then disconnect the tan wire from the computer to the relay and attach a wire to the relay terminal and ground it. If the pumps don’t run, then the inertia switch is tripped, the relay is wired incorrectly or else the relay is defective.


So you have fuel pressure, but the engine won’t start. First, rerun the electrical checks for the TFI unit and the coil from the startup section. Testing the TFI module and stator is difficult. The tests below may not always identify a defective module.

Connect a 12 volt test light from the negative coil terminal to the negative battery terminal and crank the engine. The test light should flicker as the engine cranks. The flickering test light indicates that the TFI module is probably operating correctly and collapsing the primary winding in the coil during engine crank. If the test light does not flicker, check the coil as specified below, and if the coil is OK, replace the TFI module.

Even if the TFI module is operating, the stator assembly may be defective. On one of my conversions, the stator assembly was loose in the distributor, and fired the TFI module at random times. Unfortunately, the stator is not easy to check or easy to remove from the distributor. The distributor gear has to be pressed off the shaft to remove it.

Disconnect the wiring to the ignition coil. The resistance from the positive terminal to the negative terminal on the coil should be 0.3 to 1.0 ohm’s. The resistance from the negative terminal to the positive terminal should be 6,500 to 11,500 ohm’s. Replace the coil if it is outside of these limits.

Pull the spark plugs and check for fouled plugs. Verify that all high voltage connection are in good shape. Black sooty plugs are an indication of excessive fuel. Check the fuel pressure regulator diaphragm and the MAP or BAP sensor vacuum connections. If running Speed Density, then the MAP sensor should be connected to engine vacuum. If running Mass Air, then the BAP sensor should be vented to atmosphere.


Make sure that the LEFT O2 sensor is in the left manifold. If the left and right sensors get transposed, the engine will idle rough and may also exhibit bucking type behavior about 2 minutes after startup as the computer switches to closed loop control.

Also check to see if the fuel pressure regulator diaphragm is leaking.

Clean the two connectors that attach the engine harness to the computer harness.

Now its time to get the code scanner and the timing light out. The scanners are available at most auto stores for about $35. Set the timing to factory specifications (10 degrees BTDC) with the SPOUT disconnected. Connect the code scanner and do a KOEO test and a KOER test if possible.

Work the codes as necessary to clear them. A genuine FORD Emissions Manual (Volume H) for your year harness and engine is invaluable in sorting out the codes.

Troubleshooting beyond this level is out of the scope of this article.


HO - High Output

AOD - Automatic Overdrive

O2 Sensor - Oxygen Sensor

Mass Air - 89 up Mustang 5.0’s measure air flow with a meter

Speed Density - 87-88 Mustang 5.0’s compute air flow based on engine speed and air density. Performance modifications to an SD engine are limited because fuel and air tables are stored in the computer and can’t be easily modified. In reality, the computer can handle most changes as long as the cam is not changed.

MAF - Mass Air Flow Meter

TV Linkage - Throttle Valve Linkage. An AOD uses this to determine engine load and thus shift points.

TAD Solenoid - Thermacter Air Diverter Solenoid. Diverts air pump air to the catalytic converters.

TAB Solenoid - Thermacter Air Bypass Solenoid Bypasses all air pump air during certain engine conditions.

EGR Valve Positioner - Exhaust Gas Recycle Valve Positioner. Sometimes referred to as EVP. Supplies a variable vacuum to the EGR valve as necessary.

TFI Module - Thick Film Integrated Ignition Module. This and the stator take the place of points in the distributor. It is the rectangular gray box bolted to the side of the distributor.

MAP Sensor - Manifold Air Pressure Sensor. Speed Density injection must know the manifold pressure to accurately calculate air flow into the engine.

BAP Sensor - Mass Air Flow injection uses this sensor to correct for ambient air pressure. 5.0 MAP’s and BAP’s are essentially interchangeable.

EFI - Electronic Fuel Injection. In EFI, the injectors are typically fired in banks. Truck 5.0’s are EFI.

SEFI - Sequential Electronic Fuel Injection. In SEFI, each injector is fired at a specific crank position. All 86 and up Mustangs, Crown Victorias, and Thunderbird 5.0’s are SEFI.

Serpentine Belt - An accessory belt drive where a single belt drives all accessories.

Idle Air Bypass Valve - Air bleed valve, controlled by the computer, that provides air flow for idle and cold start.

Canister Purge - Fuel vapors from the gas tank are accumulated in a charcoal canister. The purge valve draws those vapors in at engine start.

EEC - Electronic Engine Control Computer

EEC IV - Fourth Generation Electronic Engine Control Computer

EEC Relay - Relay to power EEC in Start Position

VSS Sensor - Vehicle Speed Sensor. Sensor that is bolted to transmission at speedometer cable location that senses vehicle speed. Used primarily for cruise control, however, Mass Air Injection uses VSS to stabilize idle operation.

Stator - Hall Effect switch located in the distributor.

SPOUT - TFI output signal to computer. This connection allows the computer to control engine ignition timing. When disconnected, ignition timing is fixed to the base timing as set by a timing light.

KOER Test - Key On Engine Running EEC computer test

KOEO Test - Key On Engine Off EEC computer test

AC - Air Conditioning

WOT - Wide Open Throttle

APPENDIX A Mustang Harness Connections

Based on 1988 MUSTANG wiring schematics:

When you look at the primary harness that goes from the engine to the computer, you should have 3 connectors that tie back into the main wiring harness. One connector is next to the computer and the other two are at the drivers side firewall next to the master cylinder. The one by the computer is connector #135 the two others are #201 and #403.



# 135 (The one by the computer) should have 5 active pins with a total pin count of 8. They are as follows

wire # Color Function

657 Tan Cluster EEC Malfunction Light(2.3 ONLY)

687 Gray/yellow ignition switch "RUN" Power To Oxygen Sensors

97 Tan/lt green Computer Control fuel pump relay (computer grounds this to turn relay on)

359 black/white Transmission neutral sense switch

361 red Power from EEC relay to fuel pump relay(fuel pump coil power)

#403 should again have 5 active pins with a total pin count of 8

258 white/pink low oil level sensor

348 lt green/pink thermostatic switch to AC

32 red/lt blue Ignition start Power to Distributor module

11 dk grn/yellow Tachometer gage feed from - coil connection

16 red/ lt green Ignition switch "RUN" To EEC Relay(turn on EEC in run position)

#201 should have 6 active pins with a total count of 8

33 white/pink Starter relay energized(thru clutch T to #32)

39 red/white Temperature gage

31 white/red Oil pressure gage

199 lt blue/yellow Transmission Neutral Sensor switch Return

150 dk grn/white Trans speed sensor

563 orange/yellow Trans speed sensor

787 pink/black fuel pump relay status(mass flow ONLY)

APPENDIX B Thunderbird Harness Connections

Based on 1988 TBIRD wiring schematics:

When you look at the primary harness that goes from the engine to the computer, you should have 3 connectors that tie back into the main wiring harness. One connector is next to the computer and the other two are at the drivers side firewall next to the master cylinder. The one by the computer is connector #455 the two others are #143 and #294.

# 455 (The one by the computer) should have 4 active pins with a total pin count of 8. They are as follows

wire # Color Function

97 Tan/lt green Computer Control fuel pump relay/Self Test

37 yellow Power to Fuel pump thru relay

361 red Power from EEC to inertia switch & pump relay

787 pink/black fuel pump relay status

#143 should have 8 active pins with a total pin count of 8

32 red/lt blue start power to TFI module

16 red/ lt green ignition switch "START" To Coil and EEC Relay

687 Gray/yellow ignition switch "RUN" Power To Oxygen Sensors

39 red/white Temperature gage

31 white/red Oil pressure gage

376 brown/white Ignition Switch "RUN"

657 Tan Cluster EEC Malfunction Light


#201 should have 3 active pins with a total count of 8

348 lt green/pink thermostatic switch to AC

150 dk green/white Trans speed sensor

563 orange/yellow Trans speed sensor

Background information

5) Resources

Ford Fuel Injection and Electronic Engine Control by Probst ( Most of this page is copied from here)

The HOW TO is really covered well above so I won't repeat But here are some things I did a little differently.

1) I started with a 1987 Mustang Speed density manifold and harness, and the Mass air sensor from a 1994. I got a conversion harness for $30 from interactive systems and technology . It's a do it yourself job but it was well done and the instructions were excellent, and they even covered what to do if you are installing on a non-HO motor. Order # is 800-820-082, tech number is 770-720-1259. The have many other parts for fuel injection and wiring needs. They claim an address of but it wasn't up as the date I wrote this.

2)For fuel return lines I silver soldered 1/4 ID copper tubing into 3/8 copper pipe to make a T, and put it in the vent line of my gas tank. Seems to be working well. This way if my fuel sender goes out, I don't have to make a new return location in the new one.

3) I have dual fuel tanks. I placed a low pressure high volume pump at each fuel tank. The fuel pumps each have a check valve so the act like valves when shut. I have an electric 3 way solenoid valve that switches the return lines and they are all hooked to the same switch. This allowed me to continue to use the 3 way valve I had, and the extra fuel pump was cheaper than a 6 way valve that would switch the returns and the fuel supply lines. The High pressure pump was located in the engine compartment. This arrangement meant I only needed about 3 feet of the high pressure hose. This arrangement works well when the tanks are above half full or when on flat land, but when climbing hills on a half tank or lower the engine losses power and backfires. For this reason I have ordered an accumultor tank. This is a small cylindrical tank that holds about a quart of fuel ( 5 minutes or more worth) and should solve the fuel starvation problem.[ 7/16/01, the accumulator tank works great, but I still have a problem getting the last bit from my rear tank, it's either a fuel pump problem, or a problem with the fuel pickup, I will post more when I know it.]

Additional stuff if swapping the whole motor.

I traded engines for an 88 5.0 HO engine. The install is basically taking out the one engine and puting in the other except...

The external balance ( Harmonic balancer and flexplate or flywheel are of 50 oz balance in the 5.0, only 28 oz in the 302, so if you keep the 302 belt system then you need the 302 flexplate on the engine as well.

If you go with the serpentine system.. the mustang is about 3/4 of an inch longer than the stock engine because of the water pump, and the water pump is a reverse flow version. Most people fit a flex fan in the space without problems.

For maximum cooling you can install the belt system from a Ford Explorer with the fan clutch. It will keep you very cool.

3,694 Posts
Do a search for Ford's MULTIPORT EFI WIRING MANUAL. It's actually called "Multiport EFI Engine Management Harness". It's Ford's instructions on the 5.0L/5.8L EFI conversion for Hot Rods and such. Also, if you do a search on Google for 5.0L EFI conversion or 5.0L carb to EFI... You'll find lots of info. There are a lot of '60's Bronco guys that have done this conversion. It's hard to find info specifically on Mustangs, except older 60's Mustangs. has the OEM Ford manuals on wiring. I'd get one for the year of harness that you are going to use and one for your car. They are only $12. Ofcourse a Chilton's or Haynes manual will probably work for the wiring also.

228 Posts
i am in the process of wrapping this same swap into my 95 mustang. i am using the 89 electronics, they told me it couldn't be done! i will be more than willing to share any info i have, as soon as i drive it down the road!
there are a couple different wire harness out there. i know the ford one mentioned above only has one connecter near the master cylinder and it is brown.

718 Posts
Just buy the Painless wiring setup,very easy to install but its a little on the high side

738 Posts
Discussion Starter #9
I started this thread a couple years ago when I was new to this kind of stuff...but... you could probably score a harness for a lot cheaper on Ebay or from You'll be getting a geniune ford part with no interchange problems.

Scrap yards are full of the 2.3 cars, I'm sure you could fing a harness at a scrap yard

2,011 Posts
1 - 10 of 10 Posts