Troubleshooting Brake Lights That Stay On Even When Vehicle Is Off

Question:

r brake light always on, even with key off

asked by: R J

Helpful Expert Reply:

If the brake lights on your trailer (or vehicle) remain on even when the vehicle key is turned off this tends to suggest a problem with corrosion inside the 7-way socket on the vehicle or within the Hopkins 7-Pole to 4-Pole and 5-Pole Adapter # 37385.

On an RV-style 7-way the 12V auxiliary trailer power feed is carried on the contact at the 1-o-clock position as you look at the socket on the back of the vehicle. Internal corrosion within the socket, inside the plug connecting to the rear of the socket or within the adapter could cause that 12V power to become bridged to one or more of the other contacts next to it. This could cause the vehicle or trailer brake lights to remain on even when the vehicle is off.

There are spray-on electrical contact cleaners like Caig De-Oxit that can help clean out corrosion and a small wire brush can also help to remove any corrosive build-up. If the connector is in bad shape you'll want to replace it. If yours has a round U.S. Car connector at the back you can use a replacement 7-way like # PK11893. Dielectric grease # 11755 can help protect contacts by blocking the entry of moisture and other contaminants.

expert reply by: Adam R