Gunner If you are just changing to a volt meter, connect the 2 wires from the amp meter and tape them together. This is the easiest to do. All you have to do with the new gauge is tap into the wires you taped on one side, run a ground wire to one of the ground studs, and tap into the lighting for at night driving. If you drop the steering wheel, it makes this job real easy to do.
You where asking about 12v switching. Are you adding an accessory to the car? There are extra tangs for switched voltage. Here is the thing these switchs are not ment for alot of AMPS going though them It burns out the contacts. Hide and acc board under the dash with a main fuse of 100A's couple smaller fuses of the 10-20 limit. Run a #10 gauge wire (red) to the starter soleniod on the battery side. If any thing like a Fan or Amp for a radio is used, make sure they are running on a relay. There is a BIG differents between steady flow and on and off flow when a curcuit is turned on and off. A coolant fan may use 12-15 amps when running but spike 50-60 amps to get the thing to startup for a split second
With the extra electrical I have added to #428, I have gone to a 120a charging system and a voltage meter. Good luck, unhook the battery and take your time, you will be fine.
Rick L.