Battery ground cable gauge??

[firebob]

My battery is relocated to the trunk and my ground wire has always been attached to the side of the frame at the rear of the car. Some say there can be problems using the frame and body as the path for ground to the motor. It's been that way along time but now without problems but I'm thinking about running a ground cable all the way up to the block. No peticular reason except I don't ever want to have to wonder if this is causing elect problems in the future.

I was wondering if #4 AWG wire is large enough to use for ground? The only accessories I have are the MSD box, air conditioning and a regular radio. The cable will be about 10-15ft long.

Robert

[PRRC]

We use 2 gauge to run a trunk battery ground.

[wmhjr]

We use 2 gauge to run a trunk battery ground.

You use 2 gauge from the battery forward to the engine? The OP was talking about a ground connection from a trunk mounted battery all the way forward to the block.

Frankly, I see this as pure wives tale. If you have a good ground connection from battery to frame, a solid frame, and a good connection from frame to block, I find no way to explain a ground problem at the motor. Now, the body is a different issue. I'm running a trunk mounted battery. 1 gauge from battery to frame. Good ground from frame in front to motor. I have a separate ground wire running from the battery forward to a bus bar under the dash, with multiple ground connections to that bar. MSD 6AL2 (which is in the dash) and everything else inside is grounded to the bus bar. I see no scientific reason to run another 1 or 0/1 gauge wire all the way forward. If a huge amount of solid steel (frame) can't carry the ground, you've got bigger problems IMHO.

[CarPlayLB]

You will be fine by running a ground from the frame to the block..like WMHJR said, if the frame can't carry the load, you have bigger problems!
Keep in mind that the current needs a return path back to the battery as large as the positive..i.e.if you run 1 gauge positive cable, run a 1 gauge negative cable.
Having too many grounds never hurts a thing. Most cars have rubber bushings that isolate the body, so run a ground from the frame to the body. Most guys do not run solid motor mounts, so a ground from the frame to the block is a great idea too!
More grounds will decrease the resistance and make things work better!

[6'9"Witha69]

I have 2 grounds from subframe to body. @ grounds from bod to block. I also run solid motor mounts. Trust me, there is a lot of grounding there. the body is good from the firewall back to ground everything else.

[firebob]

I guess I could've given a bit more info. The car is a 69 Firebird so it's uni-body but I have solid alum body mounts all the way and frame connectors in between sub frames so it's connected front to back. I do have rubber motor mounts though. Maybe I'll just run a cable jumper from the block to the front subframe and call it good. I'll have to check on what size I have for the positive and make the jumper the same. Thanks for the advice and opinions.

Robert

[6'9"Witha69]

I have grounding straps from the back of the heads to the firwall. Both sides. Nothing ele causes a more erratic function of electrical components than a lose or insufficient ground.

[firebob]

I also have those tiny ground wires from the head to firewall and from front sbframe to body but they are very small. Like I said I never had any probs yet but it's just one of those things that I never got around to.

Robert

[PRRC]

Really, What ever works for you. But yes still #2 in our shop. Its carry quite a load from the trunk to the motor. Grounds are the leading cause of electrical problems.

You use 2 gauge from the battery forward to the engine? The OP was talking about a ground connection from a trunk mounted battery all the way forward to the block.

Frankly, I see this as pure wives tale. If you have a good ground connection from battery to frame, a solid frame, and a good connection from frame to block, I find no way to explain a ground problem at the motor. Now, the body is a different issue. I'm running a trunk mounted battery. 1 gauge from battery to frame. Good ground from frame in front to motor. I have a separate ground wire running from the battery forward to a bus bar under the dash, with multiple ground connections to that bar. MSD 6AL2 (which is in the dash) and everything else inside is grounded to the bus bar. I see no scientific reason to run another 1 or 0/1 gauge wire all the way forward. If a huge amount of solid steel (frame) can't carry the ground, you've got bigger problems IMHO.

[wmhjr]

Really, What ever works for you. But yes still #2 in our shop. Its carry quite a load from the trunk to the motor. Grounds are the leading cause of electrical problems.

I was not being sarcastic. I was asking an honest question. Other than for plastic cars (fiberglass) without full frames, I've never seen anyone running a 2 gauge ground from a trunk battery all the way forward. Why does your shop believe that a 2 gauge cable would be a better ground conductor than a solid steel frame? That's another serious question. I'm fully aware of and familiar with ground problems.

[PRRC]

We feel that running the ground the full length from the battery to the motor is a complete circuit. It is common practice to just run the ground to the frame rail. But you are relying on all your ground circuits at that point to be grounded through the body/frame and you can have an incomplete circuit. although some accessories will ground to the body more times than not it will over heat the accessories in time and at some point fail. Now on a glass car we use American Autowires ground kit. It consist of a #10 cable and 3 jumper blocks for all your grounds to make a complete circuit. AAW suggest the cable runs a full loop back to the battery to make it a complete circuit. The cable running the full length makes it complete. we use #2 just to carry the load the extra length. Is it over kill. Maybe so. But I would rather error on the side of to much than to little. As are customers would not be happy with us if they have to return with a car that does not function as intended.
Tim

[wmhjr]

OK, I think I see the misunderstanding. I'm not suggesting that body grounds can't be a problem - especially once you start really customizing. My main question (really for those of us running either a complete frame or chassis rather than a unibody with subframes) is why run the 2 gauge? From an electrical perspective it just doesn't seem to make sense. Specifically, if I have a solid 1 gauge ground wire going from the battery to the frame itself. And I have a solid perimeter frame. And I run a heavy ground cable from the frame to at least one spot on the motor. And I run a direct ground from the battery to the MSD ignition (sure doesn't need to be 2 gauge). And I run a ground from the frame to the body (in several locations). And all gauges and electronics are grounded with a wire from the frame to a ground bus bar (and therefore not even depending on body ground) to what advantage does a 2 gauge cable run provide? From an electrical perspective, the 2 gauge will actually be less reliable than the solid frame. From a resistance perspective, it will actually have more resistance and a lower conductive capability. If the 2 gauge only goes to the motor, you haven't really solved the problem for anything not bolted directly to the motor. As a matter of fact, it's possible you made it worse by depending on the 2 gauge. Just thinking out loud.

BTW, I actually have used (most recently in my '66 Pontiac project) the grounding kit you mention along with the AAW Highway 15 harness. That's where the ground bus bar came from.

Now, plastic cars - especially those without full frames - create a completely different story.

I think we're both sort of saying the same thing - proper ground is critical. I'm just really curious about the whole 2 gauge ground from trunk to front when a full frame is in the picture. I wouldn't have brought it up but you seemed to be saying you do this for ALL cars.

BTW, thanks for the conversation. I may well be wrong here. You probably have way more experience. If so, I'd like to learn.

[CarPlayLB]

The problem that may occur with using the frame as a ground is not the frame conductivity, it is the points where the cables would attach. If the connection point comes loose or gets corroded you will have all kinds of problems. Make sure your contact points are clean to bare metal!

[wmhjr]

The problem that may occur with using the frame as a ground is not the frame conductivity, it is the points where the cables would attach. If the connection point comes loose or gets corroded you will have all kinds of problems. Make sure your contact points are clean to bare metal!

Sure. But how is that different from the ground cable coming loose in the front if you use 2 gauge? And you still need to ground the body. To be honest, I thought about running a straight ground cable up, but when I sat down and really thought about it I couldn't find any advantage for a full frame steel car. You still need to have frame and body ground connections. You're depending on a single wire rear to front to deliver the ground. The frame is a HECK of a lot bigger (ie, more conductivity) than the single 2 gauge wire. In theory, the 2 gauge could split, fray or come loose. If the frame breaks, you've got a different kind of "ground" problem. Like the one you'll be sitting on.

Still scratching my head. It just seems like some extra weight to carry around and another point of failure.

[6'9"Witha69]

Let's just say this, the more grounds the better. THe folks @ PRRC are cautious and go the extra step in ensuring there is a full loop. Is it 'necessary'? perhaps not, but should anyone ever be questioned for being too thorough? Not really. And don't look at it as another point of failure, but another failover path.

[Taman]

I agree with PRRC. The ground IS THE MOST IMPORTANT of the connections. I would run the 2 AWG wire to the front. Current runs from negative to positive. A bad positive gets youno voltage. A bad ground lets the positive float. Is it 12v or a smaller voltage. You never know. Be safe, you can't have too many grounds.

[wmhjr]

OK, I guess. I would strongly agree with it comes to unibody cars that the 2 gauge to the front makes a lot of sense. In this last build I didn't run one as it's a full frame (body off, nut and bolt project). I'm currently of the opinion that if my frame based ground (with a lot of attention to detail) is not sufficient I've got way bigger problems than a single 2 gauge cable will solve. As I said before, I truly understand the issues that a poor or erratic ground can cause. As I also said, I ran a separate (but not 2 gauge) ground directly from my rear battery to my MSD ignition, and one from my battery to my ground bus under my dash. Just not "also" a 2 gauge from battery to motor. No issue with being conservative, and that kind of detail impresses me from PRRC.

It's been an interesting thread.

[JRouche]

I have a 62 Nova with a 2x4" steel frame. Trunk mounted battery. I ran a 4/0 (0000 cable, about .46" in dia, just the copper, not the shield) welding cable up front to the starter for the positive side. I like welding cable because its flexible (many strands), great insulation because its meant for use in the welding environment and it just really inexpensive at the welding supply store.

Thats for the positive side. The ground I ran from the battery, through a disconnect switch then to the frame with the same cable.

And my frame is fully welded to the body. So all the metal on the car is at ground.

I did run a flat strap of cable from the block to the frame though. Because my engine mounts are a layered poly and steel mounts there was not a firm electrical circuit there. If you dont run a large grounding strap from the engine to the frame what can happen is the other smaller wires from the engine to frame can end up taking the engines (read starter) current.

I dont see any problem with using the frame as the grounding path. As long as you make sure to ground the engine block to the frame with some heavy cable to give the starter a return path that is NOT through the small wires that are part of the accessories of the engine, like the EFI circuits if you have that. Big no-no.

Oh, and my disconnect switch is meant to break the hot (positive) side. But I didnt like that arrangement. I would rather break the ground side. It was just easier for the placement of everything. I have that same switch on three cars and they are all on the ground... I dont know why they recommend placing it on the hot side. JR

[MonzaRacer]

As for my old Monza I ran a 2/0 welders cable from the battery in the spare tire well, to my cut off switch then another 2/0 welders cable to the chassis. My power cable was ran front to back, and I always guarded the cable well going under the car or through the fire wall.
I used 4 heavy braided stainless ground straps.
I even used 2/0 welders cable to my remote start small case GM starter.
Small grounds from hood to fire wall and fire wall to fenders and such kept my car from having unwanted electrical noises.
I used the Echlin starter solenoids from NAPA that fit Ford Rangers(as I had 2 and still had old ones, when they failed I replaced them with premium ones).
Weird to get in and start a car and it keep cranking.
The trick I like is if you kill all the grounds the car dies.I have even used in some race cars dual shut offs that open both positive and ground.

[Naps92]

Whatever ground cable you choose, I would suggest you also do a voltage test for ground connection after installing cable. It should not be more than 0.2V. Autocornerd blog has written detailed guides for that.