Originally Posted by
Nathan Plemons
As for them working the same, it is simply not true. An ammeter measures current flow and must somehow be in the circuit in a location where current flows across it. The voltmeter measures voltage and can be paralleled anywhere and the only current flowing across it will be due to the internal resistance of the meter.
This is the theoretical difference between an ammeter and a voltmeter, but the factory ammeter as Ford made it works as a voltmeter. The factory "ammeter" is in parallel with the shunt, which has a sub-ohm resistance. The gauge reads the positive or negative voltage drop across the shunt and deflects the needle accordingly.