Auto Repair Q&A



Cooling System










Auto Repair Products

Headlights Kill Brake Lights?

Headlamps (wikimedia)

Here is a fun conundrum: when the car's headlights are switched on, brake lights stop working, but when the headlights are off, the brake lights work fine. No recent repairs have been made to either lighting system.

This is the situation a forum user found himself in with his 1994 Toyota Camry LE. Two possible fixes were given by forum mechanics. The original poster has not returned to say which was the right one.

Big Block 409 posted a link for the car that is a likely fix. A lamp failure sensor in the trunk can become defective, causing lamps to stop illuminating. For this particular Toyota, that's a common issue and a relatively easy repair. "Look near the driver’s side “Pillar” or near the driver’s side “Trunk Support” for a yellow box with wires connected to it. Frequently the box can be black, or gray in color, but most times it’s yellow."

The other fix is more general and would apply to most other vehicles (or this one, if the sensor is not the problem). Posted by Jerryh20, the problem is basically a ground issue for the bulb caused by the plastic housing warping, making the ground connection loose or too light. When power is reduced (via the headlights being switched on), the ground is no longer sufficient and the tail lamps stop working. The fix is to simply remove the lamp and bend the ground contact forward so it has better contact with the lamp once reinstalled.