strip back the main outer cloth a bit and you might see the color of the individual wires - sounds like you got it wrong - the wires will go different places - one should go to engine compt, one to acc power, and one should come from the ammeter which is the power - you may also have not set up the alternator right - if it's a one wire ya gotta tie a couple wires that used to go to the regulator together, and I think one gets taped off, but too lazy to go downstairs now and try to find the info!! I think the power to the ammeter comes from the batt term on the regulator
if it's a 6cyl, how come ya got a 3position switch? thought they were all just on/off - generic aftermarket switch, or GM?
Bill
