How to Replace Trailer Light Bulbs

Verify which light is not functioning properly. With the trailer wires hooked up to your towing vehicle, depress the brakes and test both blinkers while a friend or family member stands behind the vehicle. They'll be able to see which lights work and which don't so that you don't accidentally replace the wrong one.

Test the trailer circuit before replacing the light bulb. Trailer lights and wiring are subject to much more rigorous conditions than vehicle lights due to the exposure, bumpy ride and frequent immersions (in the case of boat trailers). A circuit tester will connect to your trailer's converter plug, which is the fitting that connects to your vehicle's electrical system. A light corresponding to each wire will light up to indicate a good connection; if a light doesn't come on then you know a repair other than light bulb replacement is necessary.

Detach the trailer converter plug from the vehicle in order to disconnect power to the lights. If the circuit tests were normal, remove the light plate that covers the dead bulb. Unplug the bulb.

Take the dead bulb to your local auto parts store. This will make it easy to find a replacement bulb in a sea of different colors, models and sizes.

Plug the new bulb into the light socket. Before replacing the light plate, hook the converter plug up to your vehicle and perform the test again with a friend or family member. If the light works, unhook the converter plug and reattach the light plate.