I am hearing a lot of rules about electricity that are misused. Sounds like a few to many conversations at the bar.

It doesn't matter which way the current flow is. Cut your + or - cable and insert an ampmeter. The current is the same anywhere in that series circuit. So yes running a 2 gauge + with a 4 gauge - leaves you with a 4 gauge circuit.

We run very low voltage high current stuff at work. If I told you some simple rail circuits and how they worked you would say no way. I'm telling you WAY.

A mild steel car with good welds will carry electricity just fine as long as the connections are good. But, usually they are not. Flat washers don't penectrate and make a good connection. I cut and fix old junk all the time. There are a lot of welds that will not carry electricity well. Don't know how the car stayed together either. CHROME MOLY has trouble carrying electricity. It has carbon in it just like resisters.

My recommendation is run a #4 welding cable from the battery to the engine. Then go from that to a bulkhead. From bulkhead to the body and chassis in as many ways as possible. Use grounding washers otherwise you are pissing in the wind. I have a grounding lug on my chrome moly cage. It is just a conveneint connection point.

If you have concerns about how well a peice of tubing or any steel can carry electricity use an ohm meter and check it. For a better test. Take a 55watt headlight and run copper wires to it from your battery fully charged. Take a current reading. Then unhook the negative wire and hook to your chassis. Take another current reading. If the current is the same and the battery voltage was the same. Guess what, your car is fully capable of carrying electricity.

If you want to run big ground cables and ground busses with plenty of bonding wires it will not hurt a thing. Grounds are good. Better to be well grounded than not. There are many cars with limited grounds that do just fine. The more electronics you have the more you need good grounds.

Leon
22 years of Signal Maintaining and Signal Electronic Specialist Norfolk Southern Corp.