Brake lights coming on when hitting bumps

[joneod]

Did a quick search and didnt see this issue. I was towing an enclosed trailer at night and noticed that when I hit significant bumps, my brake lights would come on. Its both of the rear, not sure about the 3rd brake light. I had cruise and it did NOT disengage so Im not sure if its a brake pedal switch issue. Its hard to track down since it only does it on bumps. Its a 1999 Sierra (1998 body) 1 ton extended cab dually 4x4 with 6.5 diesel and 5 speed manual. Any suggestions would be greatly appreciated. Thanks

 

[Eveready]

The first test is to try it without the trailer. If the problem stops then you have localized the issue to the trailer. From that point get a tester and check the trailer wires. One of them is likely frayed and contacting a ground somewhere.

 

[kolgeirr]

Did a quick search and didnt see this issue. I was towing an enclosed trailer at night and noticed that when I hit significant bumps, my brake lights would come on. Its both of the rear, not sure about the 3rd brake light. I had cruise and it did NOT disengage so Im not sure if its a brake pedal switch issue. Its hard to track down since it only does it on bumps. Its a 1999 Sierra (1998 body) 1 ton extended cab dually 4x4 with 6.5 diesel and 5 speed manual. Any suggestions would be greatly appreciated. Thanks

Assuming you're talking about the lights on the truck reflecting on the front of the trailer, it's a pretty simple circuit. Plus, in my experience, the cruise system doesn't always do what I expect it to do.

My hunch is a brake switch. They have an internal spring that's supposed to prevent this, but they weaken with age. Plus the contacts are the cheapest garbage I've ever seen.

Given that they're $10 I'd just throw a new switch on it and see if that fixes it. If not then dig deeper into the wiring.

That said, it could be something in your trailer wiring as noted above that's somehow shorting back to kick the brake lights on. Have someone follow you over a few bumps and see if it happens without the trailer.

 

[joneod]

I appreciate the responses, I figured I would find a bumpy road to have someone follow me to check if it happens with just the truck but I was needing a direction to look. Yall pointed me in right direction.