I have a '52 GMC 450 COE. The truck is equipped with the optional Eaton electrically shifted two speed rear end. The truck was orginally 6v positive ground, I think. (Compartment for single battery under passenger seat, not a larger box for two batteries on right frame rail)Some time in the past the truck was converted to 12v negative ground. The maintenance manual makes mention of a resistor for the speedometer adaptor when used on a 12v system(makes speedometer read true in high and low). There is no mention of a resistor for the axle shift motor. I assume the 12v and 6v systems used different shift motors.
Question is, how do I know if I have a 6v motor ,if so is there a 12v replacement for it, or should I use a resistor on the 6v motor and speedo adaptor? The adaptor probably wouldn't be a big deal to find a resistor but the shift motor has big wires running to it (10-8ga) so finding something that would carry that kind of load could be a problem.
The PO (Spanky) made no mention of there being any problems with the two speed, but I haven't tried to shift it yet. I figure I'd be in it deep if I burnt the thing up. The motor is isolated from current as long as it isn't shifting. The adaptor however, sees current only when it is in low, which it is, and has been since I bought the truck. I know some people run 6v starters on12v for a long time without burning them up, but I don't want to ruin the axle by sending it 12v if there is a way around it. Thanks,
Scott

1947, 1950, & 1952 Chevrolet 1/2 ton
1952 GMC 450 series Cab Over Engine
1946 Chevrolet 2 Ton