One thing to add: THE FRAME IS NOT GROUND . On our cars the body is ground, not the frame, so if you don't run a negative cable from the battery forward to the engine block, ground it to the sheet metal in the trunk not the frame..............
Something to do with ac/dc from what I've read, but I have never seen anyone have problems with welding cable. I've used it on 4 different projects with no issues and most of my friends at the track do as well.
For the wiring from the alt. to the battery I do it like this.
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If you put 12 volts to that brown wire, you'll destroy the regulator in the alternator. That brown wire is supposed to go to the VOLTS lamp. If you use the separate switch on the battery cutoff, you need to run two wires to that switch; one goes back to the alternator, the other goes to the engine harness wire. Basically, you cut into that brown wire and tee it off to the switch in the rear. It's low current, so 16 gage wire is just fine.
Also, be sure the VOLTS lamp works, otherwise, the alternator won't produce voltage.