GM MDI the magnetic field developed by the spinning rotor in the alternator cannot develop

How you can Test a Chevy Alternator 1Test the battery voltage at the battery. Set the digital volt/ohm meter for "Volts D/C" GM MDI; and touch the meter leads to the battery terminals. The positive (red) lead goes to the positive battery terminal, and the negative (black) lead goes to the negative terminal. Voltage at the battery should be 12.7 volts.

A reading that is 12.5 volts or less indicates a discharged battery. The alternator in the Chevy can work at lower voltage levels than some other manufacturers but still requires some battery voltage to function properly.2Check for battery voltage (12.7 volts) at the battery feed wire bolted to the back of the alternator. A simple test is to attach the battery leads of your automotive circuit tester to the battery and touch the probe end of the tester to the terminal on the back of the alternator.

If the red light comes on, some voltage is present. Set the digital volt/ohm meter to " diagnostics car tool;Volts D/C" and touch the positive meter lead to the terminal on the back of the alternator while touching the negative meter lead to the negative battery terminal. The reading should be the same as battery voltage. If the alternator in your Chevy is not supplied with battery voltage, the magnetic field developed by the spinning rotor in the alternator cannot develop, and the alternator will have no voltage output.3Start the engine and test the output voltage of the alternator. With the engine running, the battery voltage should rise to 13.5 volts or higher if the alternator is functioning properly. If battery voltage doesn't rise when the engine starts, the battery tests good, and sufficient power is supplied to the back of the alternator, replace the alternator.