Troubleshooting No Power To Trailer Brakes When Trailer Connected To New GM Truck

Updated 07/15/2026 | Published 05/25/2021

Products Featured in This Question

Pollak Metal 7-Pole, RV-Style Trailer Socket - Vehicle End

(112)

$15.15

7-Way Trailer Adapter for Towing Trailers with LED Lights

(190)

$36.73

Question:

Hooked up a 2018, 2019 and 2021 GM truck to trailer and no power to trailer brakes? Blue wire Hooked up 2021 Ford F150 and no problem, Trailer brakes have power! Can you point me in the right direction to fix GM truck? All other lights on trailer work fine, just no power to Brakes

asked by: Robert P

Expert Reply:

When you hooked up to the GM trucks, did you notice if the truck said trailer connected?

The towing computer on the newer GMC trucks is kind of finicky and if it did not recognize the trailer, or the trailer was not setup in the system it will not send power to the trailer brakes.

If you were getting the no trailer connected message you will need to use the 7-Way Trailer Adapter # C57003 which has load resistors and will help the computer detect the trailer.

If the trailer was not setup in the system after being connected, you will need to do that first before the truck will send power to the brakes.

If this does not fix your issue just let me know and we can go into more in-depth trouble shooting steps.

expert reply by: Samuel C

Kelly

2/4/2025

My 2021 Chevy 4500 does not have power at the blue wire at the 7 wire connector for the trailer brakes and the dash does not say “trailer connected”. So I have no trailer brakes. Can you help?

Jameson C.

2/4/2025

@Kelly Is this a recent problem or did you just recently install a brake controller? Are the underhood connections made? Check fuses?

Kelly

2/5/2025

@JamesonC it is new truck to me that I never pulled this trailer before. I did not change anything on the trailer and I already checked under hood fuses.

Jameson C.

2/5/2025

@Kelly Any corrosion on the pins of the 7-way? Typically that can cause that. If you check out the attached link you can scroll down and see a section on some connections that need to be made to the fuse block. Check to make sure those are there. The year range on the title of the article isn't accurate by the way.

Helpful Links

faq-tb-0007-2007-2009-gm-full-size-truck-brake-control.aspx

Kelly

2/5/2025

IM not getting any responses from you but I keep getting emails that you sent a response

Jameson C.

2/5/2025

@Kelly is this still happening? Hopefully you can see this message.

Dave K.

7/13/2026

I have a 2019 GMC Sierra 2500HD. I’m hooking up to a Triton ATV trailer with electric brakes. The truck doesn’t recognize the trailer for the brakes, but all the lights on the trailer works fine. The brakes have never worked with my truck, but they do with my SUV. Do I have to buy the suggested adapter to allow the truck to send power for the brakes even though the lights are working?

Jerry B.

7/14/2026

@DaveK That's really interesting. Since the SUV is detecting the brakes but the 2500 is not, I think you may need to check your brake controller instead of going with the adapter. Is your current controller factory or aftermarket? Do you get a "Trailer Connected" notification, or any other notifications, when connecting a trailer to your truck? I'm happy to look into that more with you!

Dave

7/14/2026

@JerryB - I have a fifth wheel trailer and an ATV trailer that I tow with my GMC Sierra. The fifth wheel brakes/controller work fine when I pull it. But when I hook up the Triton ATV trailer the truck won't recognize that the trailer is connected. The truck doesn't provide any notifications when I connect the ATV trailer at all. No "trailer connection" or "check trailer wiring" type of messages at all. I ordered a 7-pin load tester to plug into the plug to test it, but I don't know how to 'fake' the trucks sensors into thinking the trailer is there so it will apply the brakes. Very weird and not sure what to do.

Jerry B.

7/15/2026

@Dave Thanks for confirming! Does the Triton trailer have LED lights? My assumption here is that your truck is not sensing the trailer's lights because their voltage is too low. With that, it does make sense to move forward with the # C57003 adapter.