Things You'll Need
Voltmeter test leads
All 12-volt lights require electrical power for illumination. The amount of voltage reaching the terminals on the rear of the 12-volt light is indicated by the brightness of the bulb. In most instances, the electrical power is supplied through a 12-volt battery. A light switch then turns the electrical power on and off. Checking the amount of voltage from the power source, along with the voltage delivered to the light bulb terminals will indicate whether the 12-volt light is good or bad.
Insert the red test lead into the voltmeter connector identified as "volt." Secure the black test lead into the voltmeter connector marked as "com." Turn the main switch of the face of the voltmeter to "DC volt."
Touch the red lead of the voltmeter to the positive (+) terminal on the 12-volt battery. Press the black lead of the voltmeter to the negative (-) terminal on the battery. The voltmeter must read greater than 12.0 volts on the display. If the voltage is less than 12.0 volts, the battery requires charging.
Remove the leads from the battery. Gain access to the rear terminals on the 12-volt light you are testing. Because 12-volt lights are utilized for many applications, consult the manufacturer's operational instructions for accessing the terminals on the 12-volt light.
Turn the switch on for the 12-volt light. Touch one of the voltmeter leads to one of the light connector terminals. Press the other lead to the other light connector terminal.
Read the display on the voltmeter. The voltmeter should read the same voltage that was displayed in Step 2. If the voltmeter display is the same voltage from Step 2, and the light does not illuminate, then the light is bad and requires replacing. If 0.0 volts is read on the display, there is a problem with the switch or the wires leading to the light bulb.
Manufacturers will offer a wiring schematic to the electrical wiring. The schematic will allow you to trace the circuit for identifying problems in the switching and wiring circuit.