Can you use a multimeter instead of a 12v light tester?

A 12v light is fine if you just want to know if there is power in that circuit, but if you want to know the exact voltage, then use a multimeter. When using a multimeter, connect the negative lead to any metal part of the car. Make sure the metal is not painted, as it may not allow the lead to make contact. Once the negative lead is connected, use the positive lead to touch the "hot" wire. With the multimeter set at 15vdc, you will then be able to see exactly how much voltage is present.