How To Check Alternator Output Voltage. Hence if you see a battery warning indicator light in your instrument panel it is always a good idea to test the voltage output of your car. Measure the Base Voltage of the Battery.
Turn the ignition key on but do not start the engine. On other systems you may need to connect the battery and field terminals using a jumper wire while checking voltage output at the battery with the engine running. What should the voltage be on a GM alternator.
Heres how to perform the test.
Take note of your voltage at the alternator 138. A diode drops a voltage of around 06 volts at low currents increasing up to. A fully charged battery should have a reading of 1265 volts. Set the multi-meter dial to AC VOLTS or DC AMPS.
