# Engine/battery grounding



## woolsey10 (Oct 18, 2011)

I recently replaced my entire electrical system and after some minor issues everything worked fine for about a month of casual driving. Then yesterday I tried reving the engine while warming up and could not push down the throttle. I noticed the throttle cable was extremely hot, smoking and melted in some spots. So I disconnected the battery and the heat and smoking stopped. I'm guessing the system decided to use this cable as a ground. I have a battery cut off switch mounted on the body just under the drivers seat. From what I understand the switch provides grounding for the battery. Is this correct or do I need to make a connection between the switch and block or frame? Also what engine grounds need to be made? This is my first attempt at wiring so any passed on knowledge is greatly appreciated, thank you.


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## woolsey10 (Oct 18, 2011)

Car is 66 lemans engine is pontiac 400


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## O52 (Jan 27, 2019)

The engine to carbody ground straps are either missing, corroded or connected to a painted surface. Depending upon year, the engine ground straps can be found between the cylinder heads or the coil bracket (as for 66 models) to the firewall. Other straps are found between the frame and front inner fenders. 
The throttle cable has now become the grounding cable which is why it smoked. Don't reuse it.


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## PontiacJim (Dec 29, 2012)

woolsey10 said:


> I recently replaced my entire electrical system and after some minor issues everything worked fine for about a month of casual driving. Then yesterday I tried reving the engine while warming up and could not push down the throttle. I noticed the throttle cable was extremely hot, smoking and melted in some spots. So I disconnected the battery and the heat and smoking stopped. I'm guessing the system decided to use this cable as a ground. I have a battery cut off switch mounted on the body just under the drivers seat. From what I understand the switch provides grounding for the battery. Is this correct or do I need to make a connection between the switch and block or frame? Also what engine grounds need to be made? This is my first attempt at wiring so any passed on knowledge is greatly appreciated, thank you.



Never heard of a cut-off switch used for a ground. The cut-off switch has the positive (+) cable go from the battery to one lug. Then the other lug would have a cable that goes to the starter solenoid - that's the only way I know of a cut-off switch being used.

There may be other ways, but that is how I wire one up.


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## woolsey10 (Oct 18, 2011)

PontiacJim said:


> Never heard of a cut-off switch used for a ground. The cut-off switch has the positive (+) cable go from the battery to one lug. Then the other lug would have a cable that goes to the starter solenoid - that's the only way I know of a cut-off switch being used.
> 
> There may be other ways, but that is how I wire one up.


That is how it is wired. What I'm saying is that the switch being metal mounted to the body that is also metal makes a ground connection for the battery. That is what the people at auto parts are saying anyway. I'm thinking that since I'm missing the necessary engine grounds my throttle cable has been the the go to ground this whole time I've been driving it and it finally got hot enough to disrupt acceleration enough for me to notice.


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## cij911 (Oct 25, 2017)

I am sure the pontiac purists will cringe, but I actually have added several grounds with gauge 0 wire. Basically from battery to block; passenger chassis to block; firewall to block. I tested the resistance of each path back to the battery to ensure proper contact points. While most will say this is overkill, it is something I have done for years with high end audio setups.


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## Lemans guy (Oct 14, 2014)

I am with Cj,....grounds have to be good. I use a large welding cable, I guess it is 0 gauge...had the auto electric shop crimp a battery terminal on one end and a big closed loop electrical connector on the other end, I go from negative ground on battery and bolt to front of head on drivers side. I route the cable down out of the way. I use all other grounds also, but this is a big solid ground engine to battery negative.


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## GTO44 (Apr 11, 2016)

I specialize is hotrod wiring. First, the correct NHRA way for a master cut off switch is thru the positive side. You can do the negative side just the same but if you ever run any classes in nhra sanctioned events it will need to be positive cut-off with the alternator going to the battery side of the cut off switch to be legal. If you never race than its not something you’ll need to worry about and either will work just fine.

For proper ground... if the cut off switch is on the ground side you need at least a 4 gauge wire from the battery to switch and switch to frame. Then you’ll want to make sure the engine and firewall are properly grounded. I always over gauge so i only use flexible welding cable and go from the engine block to the frame and engine block to the firewall with 4awg as well. If its a restomod with efi and high amp alternator i use 2 gauge welding cable and send a ground from the battery or master cut off straight to engine and branch off to the frame and firewall to eliminate RF and EMI interference. 

As far as your throttle cable melting it could be 1 of 2 things. One would be your theory. If the car is not properly grounded and the car is using the throttle cable as the main ground it could get hot. The other possibility and whats probably more likely is you have a short somewhere. And because the throttle cable is grounded thru the carb its being used as a ground source for the short and getting hot. That means somewhere in the car theres a positive 12 volt source shorting to ground. This will make any ground connection get hot enough to melt and a thin throttle cable was probably first to go. I just helped a customer break in his freshly built 408ci stroker and his alternator charging cable shorted against the block during first startup and made his thin ground strap on the back of the block to the firewall glow red hot at the bolt attachment point and it caught fire. This scenario will cause an extreme drain on the battery which is a dead giveaway of a short somewhere. 

If you’re not properly grounded than the first theory could absolutely be the cause. If the car is for sure properly grounded than look for a short somewhere...


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