Don,
What I am saying is when you disconnect the two wires on the back of the amp gauge, just connect them together with a butt connector. That will keep that circuit complete no matter where it starts or ends.
Your amp gauge is actually just “spliced” into that line. It measures current flowing along in that circuit. The current just flows through the amp meter.
Your voltmeter just needs to be connected to a good ground on one side and an “ignition on” source of power, just like a radio, etc. If it reads backwards, swap terminals on the back of the voltmeter. It works just like a multimeter does.
Pink MG40680.5044675926