How to Troubleshoot a Trailer Brake Light
- 1). Remove the taillight lens on the nonworking light. Attachment methods vary, so a slotted screwdriver, a Phillips screwdriver or a Torx driver may be needed to perform this step.
- 2). Remove the old bulb and replace it with a new bulb. Test the brake lights. Replace the lens if the bulb is operational.
- 3). Instruct a helper to depress the brake pedal and hold it. Connect the ground clip of the test light to a known good ground and probe the terminals. If the test light illuminates, move the ground clip to the outside of the socket. Should the test light stay off, the problem is a corroded socket or a bad ground connection. Clean the socket and ground connection and try again.
- 4). Probe the tow vehicle trailer connector if no power is found at the socket terminals. Finding power in the connector indicates the problem is in the trailer wiring. Reconnect the trailer plug and probe the wire from the tail lamp forward until power is found.
- 5). Start at the point where power was found and replace the section of wire to the tail light. Splice the wire using solderless butt connectors and tape completely with electrical tape.