The Stovebolt Site Forums The Shop Area The Electrical Bay 6v/12v conversion confusion

If your truck has been "converted to 12v" the person who converted it probably intended to convert it from positive ground (that the GMC 6v system would be when stock) to negative ground at the same time. I also assume that you have a 12v alternator installed. In that case:

The battery cable from the - post on the battery (the - post is smaller than the + post) should connect to the engine block. I like to use the top stud that mounts the starter motor, but being bolted to the tranny case would probably work OK.

The battery cable from the + post on the battery should connect to the large stud on the starter switch. Both battery cables should be in good condition.

My '52 GMC 12v conversion uses 2/0 size battery cables connected to the stock 6v starter. It spins the engine real fast, but you need to be careful not to leave it engaged too long. I never spin mine more than 5 seconds without letting it rest.

The 6 volt lamps will burn out very quickly when exposed to 12v. They should all be replaced with 12v equivalents.

If you are still running points-type ignition you need either a stomp starter switch with a small lug on the side (my preference) or a coil marked something like "12v, no resistor needed".

The only real difference between small trucks and your 451 is the length of wires going to rear lighting. If you know which end of a soldering iron to hold and how to use shrink wrap making your own harness for these simple trucks isn't that hard to do. It must be easy because I did it on mine.