Troubleshooting Brake/Turn Signal Lights Only Flashing On Trailer When Headlights Are Off

Updated 02/05/2024 | Published 02/04/2024

Question:

2019 VW Jetta. Trailer lights do not flash/brake when car lights are on. Although when car lights off, the trailer lights fully function.

asked by: Donald

Expert Reply:

It sounds to me like the lights on your trailer are wired up incorrectly. The Running/Brake lights will typically use 2 separate filaments inside a bulb. The brighter should be for the brake/turn signals and the lighter for the running lights. If they are wired backwards it is hard to see the less bright light flash when the brighter lights are on. This is what it sounds like is happening on your trailer.

There is another chance that the lights are shorting out. If that is the case your side clearance lights would flash with the turn signals or come on with the brake lights.

If neither of these is what is happening please let me know what parts you have installed on either your 2019 VW Jetta or trailer.

expert reply by: Bud M