Troubleshooting Brake Light That Comes on with Varying Brightness

Question:

Why would this brake light come on dim sometimes and other times exhibits normal brightness?

asked by: Rolf S

Expert Reply:

When a trailer light exhibits varying brightness this is usually caused by a grounding issue. If a trailer's main ground is marginal (say for example if it is attached to a rusty spot on the frame) it may pass enough current for some light functions to work properly but not others. Similarly, if the light in question uses its mounting hardware as the ground, rust, grease, primer and paint at that mounting point could cause the same grounding problem. Cleaning the grounding point and re-installing the ground wire usually does the trick.

The place to start is at the main trailer ground wire. Make sure this is tightly affixed to a clean bare metal spot on the trailer frame. Check each brake light's wiring too, looking for loose wiring connections of loose mounting hardware and correct as needed.

Once you have found and corrected the issue you can protect the connections from corrosion by applying dielectric grease like # 11755 which block the damaging effects of moisture from interfering with your light signals.

expert reply by: Adam R