Why Do My Trailer Brakes Apply When The Hazard Lights Are On?
Updated 05/27/2026 | Published 05/23/2026
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Question:
The trailer brakes are applied through the brake controller when the hazards are turned on. The cold wire has power when the brakes are applied and when the hazards are turned on. Do I need to install a pulse preventer or is there a new brake controller that would solve the problem without adding a preventer?
asked by: Christopher H
Expert Reply:
Hello Christopher,
Since this is on a 1992 GMC pickup, what you are running into is pretty common with the older GM brake light wiring design. The cold side of the brake switch on those trucks can carry the pulsing hazard light signal, which causes the brake controller to think the brakes are being applied anytime the hazards are flashing.
The Tow Ready Pulse Preventer # 5501 that used to solve this issue has unfortunately been discontinued, so there is not a direct replacement currently available through us. If you are able to track one down elsewhere, that would still be a good solution.
If not, I would recommend upgrading to the Curt TriFlex NEXT Trailer Brake Controller with Plug-In Harness # C67PQ. The newer proportional controllers like this tend to handle the older GM wiring systems much better than many of the older time-delay controllers. The TriFlex NEXT also gives you much smoother trailer braking overall and is a really solid upgrade if your current controller is older.
That said, depending on the exact wiring condition of the truck, some older GM models can still occasionally need additional wiring isolation, but I would definitely start with the newer controller first before trying to chase down a discontinued pulse preventer.
What brake controller are you currently using in the truck now?
