Ford Mustang Forums banner

1 - 20 of 34 Posts

·
Registered
Joined
·
16 Posts
Discussion Starter #1
After 30 years I tracked down the car I had in high school and am now restoring it. The latest issue is the heater blower motor. Someone had replaced the original 3 wire motor with a 2 wire. It did work, but of course only had one speed. I pulled the heater box, replaced the core, put in the correct 3 wire motor from C J Pony, resealed the case, and reinstalled. When I tried it, it blew the fuse. Thinking maybe I had a clearance issue with the squirrel cage, I pulled it back out. It's fine, no clearance issues. I had tested the motor on the bench with a battery before I put it in the car, and it worked fine on both low and high speeds. After mounting it back in the car, but before I connected the wiring, I put in a new fuse and checked for 12 volts at the firewall red and orange connectors. With the blower switch on low I got 12 volts on one wire, and with the switch on high I got 12 volts on the other wire. So I reconnected the wires and tried it again. Blew the fuse. Next I went back to basics. With the heater box still in the car, I eliminated everything and used jumper wires to go directly from the motor to the battery. Black wire to negative, red or orange to positive. Nothing. Then I got a second battery, set it on the fender, hooked it up the same way. Motor runs fine on both low and high speeds. After scratching my head, I went back to the car battery, and yes the car does start and run fine with that battery. I disconnected the positive battery lead and tried the jumpers again. Nothing. I put the positive lead back on and disconnected the negative lead. Motor runs fine on low and high speeds. What's going on?
 

·
Registered
Joined
·
23,260 Posts
what are the 3 wires?

is there a short in one of the 3 wires, and that is why someone put a 2 wire on?
 

·
Registered
Joined
·
16 Posts
Discussion Starter #3
1964 1/2 and 1965 Mustangs have 3 wire heater motors. One is ground, and the other two are low and high speed. The motor has two different windings. In 1966 they went to a resistor style of switch to control the two different speeds, so that motor only has a single winding with just a ground and hot wire. (known as a two wire motor).
 

·
Registered
Joined
·
23,260 Posts
2 positive and 1 ground

now answer the second question
 

·
Registered
Joined
·
16 Posts
Discussion Starter #5
No shorts in the wires. As I said in the first post voltages read normal. Can't say why someone else did what they did.
 

·
Registered
Joined
·
23,260 Posts
I am telling you why someone did what they did, cause they ran into the same situation, and could not diagnose it

In order to blow a fuse,

THERE IS A SHORT

OR

THE motor is drawing too much current, you tested,

Was the current the motor was pulling higher than the fuse, you need to measure current.

no other possibility

So now that we have established there is short, or overcurrent, and your tests were not adequate into finding it, tell me exactly how you checked for voltage, where the leads went exactly.

and I will show you, that your process to diagnose was a little off.
 

·
Registered
Joined
·
16 Posts
Discussion Starter #7
Wiring for the blower motor is about as simple as it gets. From the fuse block to the switch. The switch has three positions, high,off, and low in that order. From the switch through the firewall with the low and high speed wires direct to the motor. I measured 12 volts at each of the two wires as I moved the switch from high to low. Today I had the same thought about the amp draw of the new motor as you did. I tested it again with the jumpers direct to the battery, but put a 14 amp fuse in line. It ran fine and did not blow the fuse. What doesn't make sense is that the 2 wire motor was working, but just at the one speed using the same wiring. Of course only one of the switch positions made it run.
 

·
Registered
Joined
·
23,260 Posts
are you ready?

or do you want to keep telling me how easy this is, yet it keeps blowing fuses?

when you measure voltage at a end of a wire that is only 1/3 of the circuit.

there is NO current flowing, therefore no fuse will blow, with 0 amps flowing

hook a test light to battery positive

then touch the ground wire leaving the motor.

what happens?
 

·
Registered
Joined
·
16 Posts
Discussion Starter #9
Battery connected, new fuse, wires from heater switch to heater motor disconnected, key off, heater switch off.

Positive battery post to heater motor ground.................................................................test light on.
Positive battery post to either heater wire from heater switch..........................................test light off.



Key on, heater switch moved to either Low or High.

Positive battery post to either heater wire from switch...................................................test light off.
Negative battery post to either heater wire from switch..................................................test light on.



Key off, heater switch moved to either Low or High.

Negative post to either heater wire from switch.............................................................test light off.



Key on or off.

Positive battery post to any of the 3 heater motor wires..................................................test light on.


That last one doesn't look right to me. New motor bad?
 

·
Registered
Joined
·
23,260 Posts
in your last test, are the wires off the motor not connected to anything?
 

·
Registered
Joined
·
16 Posts
Discussion Starter #11
That is correct. The two positive motor wires are not connected to anything. The ground is connected to battery negative.
 

·
Registered
Joined
·
23,260 Posts
I meant all three, including the ground.
 

·
Registered
Joined
·
16 Posts
Discussion Starter #13
Are you asking me another question? In the last test the motor ground is connected to the battery negative. Neither Low or High speed leads are connected to anything. The test light is from the battery positive to any of the three wires. Result is the same for all. Light is on.
 

·
Registered
Joined
·
23,260 Posts
disconnect the wire going to battery negative repeat test.

dc, brushed motors, will always do what you got.

that is how it the motor goes round and round.

so remove ALL, wires and redo.

then we will move onto the next test.
 

·
Registered
Joined
·
16 Posts
Discussion Starter #15
Sorry, not sure which test you want me to redo. The only wire connected to anything now is the ground wire to the battery. You want me to disconnect that ground from the battery and then check what? If the battery is disconnected from the motor there will be nothing to power the test light. Please clarify.
 

·
Registered
Joined
·
23,260 Posts
is the motor mounted in the car or not?
 

·
Registered
Joined
·
16 Posts
Discussion Starter #17
Yes. It is in the heater box, and mounted in the car as it will be in it's final position.
 

·
Registered
Joined
·
23,260 Posts
disconnect the ground wire and retest, then
 

·
Registered
Joined
·
16 Posts
Discussion Starter #19
Ok, I see now. The motor still gets a ground through the mounting bolts. Removed the ground wire from motor to battery. All results remain the same.
 

·
Registered
Joined
·
23,260 Posts
and is the light as bright as without the motor?

ie 2 loads in series will cause a voltage drop across each load.

now I have no idea if the motor should be grounded through mounts, but I think not.

therefore, we have shown

looking at wires will not always reveal a short

you actually have to test the invisible electrons.
 
1 - 20 of 34 Posts
Top