60 valiant gauges

The temp / fuel problem is separate from the ammeter

I don't know where the instrument voltage regulator/ limiter is on a '60, it might be in the fuel gauge or a separate unit

The ammeter sounds like another problem, and could be a lot of things


Bad connection in the ignition feed to the regulator, bad alternator, bad regulator, bad ground on the regulator, bad connections in the bulkhead connector. I believe that the battery main feed and charging line on yours goes through the firewall separately form the other bulkhead connector

MAKE UP a great big long clip lead about 4' long with no12 wire. Connect from the battery pos to the regulator IGN terminal temporarily and see if the problem is helped.

Make up a big wire, either no 10 or three no 12's in parallel, and connect your alternator output stud directly to the battery hot. Your ammeter will not work, but compare VOLTAGE at the battery before and after you do this to see if the problem changed If it helps, you have problems in the battery charge lead/ ammeter circuit, possibly the ammeter itself

Also run the engine at night in a dark spot, raise the hood and look at the alternator. IF you see sparks inside the alternator NOT FROM the brush area, but IN the windings area, the windings have come loose and are shorting internally.

IF the above does not cure the trouble, I'd replace the regulator WHICH IS A GUESS, and last the alternator.