[Accelo]

The wiring size it critical, as it determines the resistance and thus the voltage drop. A larger wire size will not work unless the gauge taps are much further apart. I mean a lot further. The gauge is labeled Amps but it actually measures millivolts or 1:1000 of a volt. It is a volt gauge measuring voltage drop in volts. Full scale deflection is less than 1 volt. This circuit is know as a shut. Both sides of the amp meter are +, no grounds. Most convert the gauge to volts as a work around for this issue. I know the 67-72 truck guys do anyhow. I am unsure what is feasible for your 1963 truck. Do you still have the correct amperage fuses that are in the power to the gauge? Should be one on each leg. I thought they were 2A but I wouldn't trust that figure without looking it up.