Things You'll Need
You go out to your automobile or boat and try to crank the motor, only to get that ominous clicking sound from the alternator that signifies a dead battery. The battery was charged when you left it a few hours ago, but now it's dead. The problem could be the battery itself, or it could be that a short somewhere in the vehicle's wiring is draining the battery while it sits idle. You can measure the amount of power drain coming from the voltage regulator and narrow down the problem.
Disconnect the connection from the positive terminal on your vehicle's battery using a wrench. Leave the negative cable connected. The idea is not to disconnect the battery from the vehicle, but to insert the multimeter into the battery circuit.
Power on your multimeter and set the dial to the highest amp setting. Refer to the instruction manual of your multimeter if you are unsure how to do this.
Connect the negative terminal lead on the multimeter to the positive battery cable using the alligator clip or probe. Connect the positive lead on the multimeter to the positive terminal on the battery.
Reduce the setting on the multimeter to the lowest setting. Watch the readout on the multimeter for a reading. If there is a reading over 50 milliamps, then there is a short somewhere in either the wiring or an electrical component.
Disconnect the voltage regulator from the vehicle, using the instructions in your vehicle's service guide. Check the readout on the multimeter. If the drain stops, then the voltage regulator is faulty. If the reading remains the same, the problem is somewhere else in the wiring.
Pay attention to the order you are connecting the leads on the multimeter to the battery and battery cable.
Do not allow the positive connection going to the battery touch any metal part of the vehicle. Otherwise you will short circuit the connection and may damage your vehicle's electrical system.