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Discussion Starter #1
I have a few questions regarding wiring my new Holley EFI and grounding.

Have a trunk mounted battery currently with a 2/0 ground cable running thru car to the engine block and a 2/0 ground from battery to unibody in hatch. Is the 2/0 ground necessary or will it cause issues with the Holley EFI?

Note: I am using LS Coil Near Plug Ignition Coils NOT FORD TFI any longer. Also 2 ground straps from block to frame.

And the last question, do I follow Holley's Instructions and wire main 10 Ga power and ground straight to battery terminals? Or just positive to terminal and ground with a short lead to a solid point on body?

Thanks and any definitive answers are appreciated!
 

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Cannot answer the ground question but when asking Holley tech about Sniper he interrupted me a few times and make sure negative is to battery itself and not to ground. No idea why but i am willing to learn
 

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I don’t have a Holley but a pro m system. They wanted me to run battery ground to block. On the same spot put the ecu ground. Make sure you still have another spot for block to passenger side fender and finally the braided ground in back.

I know they are different systems but same principles apply.
 

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Discussion Starter #5
Any other suggestions before i just ground Holley EFI to battery and run a 2/0 ground cable from battery to block?
 

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Is there only 1 ground??
 

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Discussion Starter #7
Is there only 1 ground??

1 main 10GA ground that Holley specifies to ground directly to battery.

1 ground for LS coils to head

1 ground for Holley EFI Wideband Harness to head

various grounds for fuel pump and LS coils relay
 

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The last thing you want to do with any sensitive electronics is ground to the battery. It is a terrible idea no matter who says it is good. It is especially silly if you run a single wire from battery to engine for a ground, and I can prove why this is all true.

If someone insists on grounding at the battery, at least have enough sense to not go to the post or the heavy lead directly. The negative from the ancillary gear (which would include all aftermarket electronics) should go back to the chassis right near the battery, and then a bond made from that solid ground point to the battery.

The purpose of this is to prevent noise and to prevent equipment damage and possible negative lead fires if you lose the negative battery lead main ground.

With a unibody or a caged car, the battery should have a good solid ground reliable to the chassis. The chassis then becomes the ground centric point. You can run a start and charge ground cable to the engine, but if you get a good enough bite on thick sheet metal the chassis itself will have far less resistance and a lot less noise impedance than any copper cable to the front you could manage. The block, of course, also has to well grounded in this case to heavy solid sheet metal.

My Holley EFI positive runs back to the trunk battery **with a fuse near the battery** . I initially ran my Holley negative back there to the battery negative, but I had noise issues. I grounded my Holley to the firewall near where Ford grounded the EEC IV signal and digital power grounds (they ground only injector returns up to the inner fender near the battery) and it cleaned right up. The firewall became my common ground point for signal grounds, and the front frame rails the block ground point.

If you ever run a long ground to a battery post, or a long positive wire to the battery without a fuse or fuse link at the battery, you have no fault protection. It isn't a smart thing to do.
 

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Discussion Starter #9
The last thing you want to do with any sensitive electronics is ground to the battery. It is a terrible idea no matter who says it is good. It is especially silly if you run a single wire from battery to engine for a ground, and I can prove why this is all true.

If someone insists on grounding at the battery, at least have enough sense to not go to the post or the heavy lead directly. The negative from the ancillary gear (which would include all aftermarket electronics) should go back to the chassis right near the battery, and then a bond made from that solid ground point to the battery.

The purpose of this is to prevent noise and to prevent equipment damage and possible negative lead fires if you lose the negative battery lead main ground.

With a unibody or a caged car, the battery should have a good solid ground reliable to the chassis. The chassis then becomes the ground centric point. You can run a start and charge ground cable to the engine, but if you get a good enough bite on thick sheet metal the chassis itself will have far less resistance and a lot less noise impedance than any copper cable to the front you could manage. The block, of course, also has to well grounded in this case to heavy solid sheet metal.

My Holley EFI positive runs back to the trunk battery **with a fuse near the battery** . I initially ran my Holley negative back there to the battery negative, but I had noise issues. I grounded my Holley to the firewall near where Ford grounded the EEC IV signal and digital power grounds (they ground only injector returns up to the inner fender near the battery) and it cleaned right up. The firewall became my common ground point for signal grounds, and the front frame rails the block ground point.

If you ever run a long ground to a battery post, or a long positive wire to the battery without a fuse or fuse link at the battery, you have no fault protection. It isn't a smart thing to do.



Awesome, thanks for the info!

Ill be removing the 2/0 cable from battery ground to block and use it to replace the smaller gauge, current, ground wire from battery to chassis. Also will be grounding the Holley EFI near the firewall where Ford originally grounded the EEC IV.

And while you're here what kind of/size fuse or circuit breaker do you recommend to fuse the main positive battery lead running from battery to front distribution block in driver fender? Have a 200A alternator if that means anything. Will be using a 200A Fuse in the alternator charging lead.

Also, any suggestion on to exactly where i should solidly ground the cable from battery to on my hatch? its currently just grounded to the floor pan right next to the battery from the previous owner.(pic attached)

Thanks again for the extremely helpful information!
 

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Awesome, thanks for the info!

Ill be removing the 2/0 cable from battery ground to block and use it to replace the smaller gauge, current, ground wire from battery to chassis. Also will be grounding the Holley EFI near the firewall where Ford originally grounded the EEC IV.

And while you're here what kind of/size fuse or circuit breaker do you recommend to fuse the main positive battery lead running from battery to front distribution block in driver fender? Have a 200A alternator if that means anything. Will be using a 200A Fuse in the alternator charging lead.

Also, any suggestion on to exactly where i should solidly ground the cable from battery to on my hatch? its currently just grounded to the floor pan right next to the battery from the previous owner.(pic attached)

Thanks again for the extremely helpful information!
Car wiring is not any different than other wiring, it is common sense. You have to fuse any wire leaving a high current source as close to the source as possible, and that fuse has to be be reasonably above the peak load current and safely below the wire current rating. This is so if that wire is shorted or overloaded the breaker or wire opens and does not cause a fire.

Holly, at least in my installation, fused at the ECU. That means the wire up to that fuse is unprotected.

You should use a similar or just slightly larger fuse or breaker back at the source. Either duplicate what Holley uses or go up just to the next step up in size.

If you use the alternator lead at the alternator, it protects the alternator. But that protection is actually sort of meaningless. If you get a reverse battery or some load fault the alternator diodes or field winding will usually pop anyway. I wouldn't remove the fuse, it isn't bad to use one, it just does not make the wiring safe.

The real place to protect the alternator high current feed is at the battery connection end. The battery can dump hundreds and hundreds of amps for a long time, whether the car is off or on. In a hard short it will run until the battery melts down, a wire burns in two, or the short burns open. This is why car manufacturers use fuse links where they up-tie a branch into a higher current feed.

Be sure you protect the wires at the SOURCE, and that between the protection an the source things are no where a wire fire would cause a car fire. The alternator is a source when running, so it isn't bad to protect there. It just doesn't do much unless the wire leaving the protection is rated way above the protection size. The real issue is the battery. It can dump 10 or 20 times what the alternator can. If you have a wire from the alternator to the battery the fuse at the alternator doesn't do a single thing to make you safer. It just might help the alternator, but it won't stop a fire at all. Any fuse or fuse link belongs near the battery ends any lines or line branches.
 
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1 main 10GA ground that Holley specifies to ground directly to battery.

1 ground for LS coils to head

1 ground for Holley EFI Wideband Harness to head

various grounds for fuel pump and LS coils relay
That is what i thought

They dont tell you which are output grounds, sensor grounds, or if they connect internally within the ecm

Following TomR’s recom will be a significant improvement over what Holley is saying
 
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Discussion Starter #12
Car wiring is not any different than other wiring, it is common sense. You have to fuse any wire leaving a high current source as close to the source as possible, and that fuse has to be be reasonably above the peak load current and safely below the wire current rating. This is so if that wire is shorted or overloaded the breaker or wire opens and does not cause a fire.

Holly, at least in my installation, fused at the ECU. That means the wire up to that fuse is unprotected.

You should use a similar or just slightly larger fuse or breaker back at the source. Either duplicate what Holley uses or go up just to the next step up in size.

If you use the alternator lead at the alternator, it protects the alternator. But that protection is actually sort of meaningless. If you get a reverse battery or some load fault the alternator diodes or field winding will usually pop anyway. I wouldn't remove the fuse, it isn't bad to use one, it just does not make the wiring safe.

The real place to protect the alternator high current feed is at the battery connection end. The battery can dump hundreds and hundreds of amps for a long time, whether the car is off or on. In a hard short it will run until the battery melts down, a wire burns in two, or the short burns open. This is why car manufacturers use fuse links where they up-tie a branch into a higher current feed.

Be sure you protect the wires at the SOURCE, and that between the protection an the source things are no where a wire fire would cause a car fire. The alternator is a source when running, so it isn't bad to protect there. It just doesn't do much unless the wire leaving the protection is rated way above the protection size. The real issue is the battery. It can dump 10 or 20 times what the alternator can. If you have a wire from the alternator to the battery the fuse at the alternator doesn't do a single thing to make you safer. It just might help the alternator, but it won't stop a fire at all. Any fuse or fuse link belongs near the battery ends any lines or line branches.



Sounds great! Will just use a fuse right at battery for main 2/0 cable to front distribution block and will add a secondary fuse at battery for main Holley EFI power.

Thanks for the help!
 
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