Blinking Brake Lights

[Gdattilo]

Hi, I had an odd situation the other day. I had my 2020 2970RL home and connected to my truck overnight. When I got up the next morning to move it, I noticed that my brake lights were blinking very fast but only at about 1/3 of normal intensity. This was before I unlocked or started my pickup. Any thoughts as to what would cause this? I unplugged the cable to the truck and it stopped and I can not duplicate it.

Any thoughts would be appreciated.

Gus

[traveldawg]

Hi Gdattilo. Welcome to the forum. It might help if you could tell us the make of the truck. I know Ford and Chevy handle braking connections differently. And I know of one instance where a 2020 chevy needed an adapter for the brake system to work correctly (much like the early model chevys) but that was on a rig with disc brakes.

And I'm wondering if you did any troubleshooting before unplugging the trailer. Like: step on the truck brakes to see what happened, starting the truck, trying the blinkers, etc.

For now I'd suggest checking the connectors to be sure they look ok. Or maybe leave it plugged in again to see if the same thing happens.

We'll see what other have in mind. Folks here sure have a lot of experience.

[powerscol]

Some trucks have a battery isolater module built in so if left plugged in the trailer cant drain the truck battery down. Perhaps is was doing its job but cycling. However why it was powering the brake lights is a mystery - unless it was flashing an error code. Do you have an aftermarket controller? if so look in their manual or your truck manual if it has a built in brake controller.

Please post back what you find

Good luck

[Gdattilo]

Hi Gdattilo. Welcome to the forum. It might help if you could tell us the make of the truck. I know Ford and Chevy handle braking connections differently. And I know of one instance where a 2020 chevy needed an adapter for the brake system to work correctly (much like the early model chevys) but that was on a rig with disc brakes.

And I'm wondering if you did any troubleshooting before unplugging the trailer. Like: step on the truck brakes to see what happened, starting the truck, trying the blinkers, etc.

For now I'd suggest checking the connectors to be sure they look ok. Or maybe leave it plugged in again to see if the same thing happens.

We'll see what other have in mind. Folks here sure have a lot of experience.

Hi Traveldawg and thanks for the reply. I have a 2020 GMC Sierra 2500HD and I did not do any diagnostics prior to the disconnect. On thing I have learned that I did not mention is that the Trailer power cord is tied inrto my truck alarm. I found this out by disconnecting the cable while my truck was locked and it set my alarm off. It may be tied into that?

[Calbar]

Hi Traveldawg and thanks for the reply. I have a 2020 GMC Sierra 2500HD and I did not do any diagnostics prior to the disconnect. On thing I have learned that I did not mention is that the Trailer power cord is tied inrto my truck alarm. I found this out by disconnecting the cable while my truck was locked and it set my alarm off. It may be tied into that?

Sounds like either the alarm flashes the lights to show activated or when you hit the button to open the truck it flashed brake lights to show that the truck alarm was disabled and the doors were unlocked. My 2019 RAM 3500 flashes lights when I lock and unlock and so did my 2009 Tundra. I use this feature to check that the lights work. Makes it easy for me to do a light check by myself.

Rob

[traveldawg]

Every bit of info helps. I guess some more testing may be in order with the alarm. Of course, the simple thing to do is to just disconnect the trailer if you're going to leave it connected overnight. Sometimes I do that and on older trailers years ago before all these fancy trick controller circuits I always disconnected the connector if I didn't unhitch for the night.

[bhop56]

As stated above with GMs, if there is a bad or weak light and socket connection or light out, it can cause that signal light and or other lights voltage to vary.
I just sold a GMC Sierra 2500 that was consistent with this. Believe it or not I found the culprit to be too much "light bulb lube" used when I changed the last running light and signal bulb on that side of the truck. You can't make this stuff up!

[Hokitect]

I also have a 2020 GMC Sierra 2500HD and noticed the same issue on my new Reflection 150 290BH. When the trailer wiring harness is connected to the truck and the truck is parked and locked, the brake lights flash in a regular pattern. This appears to be part of the ProGrade trailer package.

The below is from GMC’s website:
- Trailer Theft Detection extends your truck’s theft alert capabilities to the trailer (if equipped). This is enabled through the settings in the in-vehicle trailering app.
- When enabled, parked and the trailer electrical connector is disconnected, your truck’s lights flash and its horn will sound (if your truck is turned off).

This is specific to GMC and Chevy vehicles with the ProGrade Trailering Package, not an electrical gremlin.