Quote:
Originally Posted by jg61hawk
I bought a disconnect switch locally, the type with a big turn dial OFF/ON. They only had normal 12volt wire in the store. I am breaking the POSITIVE ground. Will it matter if I run the 12volt wire from the frame to the disconnect and then the good 6 volt wire from the disconnect to the battery?
Do ground wires carry current or is just the Negative wire from the battery to the starter the important one?
If the answer is the ground wires need to be 6 volt, do they make a 6 volt disconnect versus a 12 volt disconnect?
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Hawk - Wire doesn't really care 6V vs. 12V, it cares about amps. You should have the wire the same size (same gauge) going into the switch as going out. For the Model A, this means you run the thick cable (the one that's the size of your finger) to and from. The original Model a ground was a solid strap but many cars now use a flat braided strap for the ground.
Disconnect doesn't care 6V vs. 12V either. It's also all about amps. You need to look at the disconnect and see what amperage it's rated for. Since you'll be putting starting amperage through it it needs to be rated on the order of several hundreds of amps. If it's designed to be used as a primary disconnect you'll likely find that the terminals are quite large - like 1/4" or 5/16" (the posts, not the nuts). If they're tiny then this is likely not designed to be used as a primary disconnect.
BTW, on a disconnect installation, it's much more common to interrupt the power side, not the ground side. You should interrupt the big honkin' power wire from the battery (negative) to the starter, the power to the rest of the car is distributed from there (the yellow wire that goes up to the terminal box on the firewall).
To answer your other question, yes both negative and positive wires carry current. Think of the wiring as being a closed loop from the negative side of your battery to the positive side. For everything to work, you need to send amps from one terminal to the other. You lose amps along the way if they take an alternate path to ground (like light bulbs grounding against the headlight socket) but for the most part you should consider that both sides need equal capacity. (As an aside, house wiring works the same way - that's why the black wires and the white wires in a wall plug are the same size. I know that's oversimplification and there are cases in house wiring where white wires can be shared between black/red wires of different phases, but that's because house wiring is AC, not DC like the Model A. So let's not go there
).
JayJay