Troubleshooting Wiring on 2004 Chevy Dually That Activates Trailer Brakes When Hazards Are On

Question:

When I use the 4way flashers or the right turn signal the trailer brakes come on

asked by: David S

Expert Reply:

It sounds like you could have a corrosion issue in either the truck's trailer socket or the trailer's plug.

What can happen is that corrosion can build up inside the socket or plug and cause two circuits that are next to each other to become bridged together. If you refer to the linked photo of a 7-way trailer socket you'll see that the brake circuit at the 5-o-clock position is next to the right turn/stop circuit at the 3-o-clock position. Chances are that either the truck socket or the trailer plug has corrosive build-up that is joining those two circuits. This would explain why the hazard lights and right turn light activate the trailer brakes.

Sometimes corrosion can build up inside the socket or plug where it can be tough to see and even harder to clean out. You can try cleaning out the connectors with a spray-on electrical contact cleaner but if you need to replace them you can use 7-way socket # HM40975 on the truck. If you need to replace the 7-way plug on the trailer an easy way to accomplish this is to use a junction box with pre-wired 7-way plug, # HS381-9000, along with ring terminals # 44-5310A for making the connections inside the box.

A good method for blocking the formation of corrosion is to use dielectric grease # 11755 inside the connections. This grease blocks water and other contaminants from getting inside your connectors.