I don’t mean that it sounds crazy or not correct. I mean it is physically impossible to connect +5 and -12 (or any other voltages) together and have them not read the same voltage, they’re at the same potential. I Don’t know what voltage it would be but they can’t be different. You have to be missing something. Take one of the cars that you think has +5 and -12 connected together and put a jumper from +5 to -12 on HB1 pins 2-3 or on one of the J plugs on the Buss Board pins 2-3 and see what happens.