Originally Posted by jerryc41
Right, but I don't want to connect the hot wire to the ground on the brakes, and vice versa.
One wire from the B-A switch will go to power, and the other will go to one of the brake wires, but which one?
Go to Radio Shack and buy a cheap VOM, which is a volt-amp-meter.
It will also have a resistance measurement settings as well.
They are cheap, informative, andd you will wish you bought one 20 years ago.
When you have it, measure the reistance to ground from each wire.
The wire that says ZERO ( 0 ) is the ground. The other wire will be a low resistance in the order of one (1) ohm or so.
Ohm,is a unit of resistance measurement.
Now you can check AC, DC voltages and resistance of many things in your trailer as well as your tow vehicle and home.
Otherwise your question can go on and on and on, and all without an answer.