I am not a GMC expert but I am almost certain 1948-53 GMC's came with this color gauges. If not I know some Chevrolet Forward Control trucks used this style gauges much later than 1953. That may mean the gas gauge could be 12 volts and a 60PSI oil gauge.
Tim, there are two gauges that have terminals on the back, temp and amp. The square connection closest to you is the mechanical oil gauge connection.
Brokenhead, ammeters do not care if they are 6 or 12 volt, the gas gauge does for sure.
