In the classic generator or alternator power circuit, all of the output went through the gauge for an accurate indication of how much the generating device was working against the load of the electrical system items. Of course, the voltage regulator is a part of this circuit, too.
That was fine when the outputs of non-police vehicle generating devices was under abt 60 amps. BUT as the vehicles age, the gauges can age, too, which can increase resistance and resistance builds heat. Too much heat can make for other things to happen, too.
In abt 1972, Chrysler changed the charging circuit to run the alt gauge via a shunt, where the gauge would indicate only a little of the total charging activities. Which meant the needle didn't move nearly as much, but it did move. By abt 1976, heated rear windows were popular, which came with factory 100amp alternators to run them.
In abt 1970, GM started to phase-in voltmeters rather than ammeters into their vehicles. Claiming that it gave a better indication of the charging system's health. At the time, I didn't really believe that, as i wanted to see if the system was charging and how much, rather than looking at a voltmeter. But I adapted.
There are several threads on the "ammeter bypass" procedure and the reason for it in these forums. Prevention of instrument panel fires is a major reason for this procedure. Not hard to do.
Take care,
CBODY67
