Troubleshooting 12v Power on 7-way Trailer Plug of 2003 GMC Sierra Not Working

Updated 09/23/2024 | Published 03/18/2021

Question:

.I have a 2003 GMC Sierra 1500 and my 7 pin doesn’t have 12 volt power so my new Curt Echo won’t power up. How can I get 12 volts to my connector? Thanks

asked by: Joe M

Expert Reply:

It sounds like this could be as simple as a missing fuse that activates the brake controller power or just a bad ground wire, but it does depend on whether or not this is a factory installed 7 way. I would start just by making sure that the ground wire is connected to a rust and debris free spot on the vehicle frame.

If the 7 way is the factory plug, then there's likely an issue along the power wire running from the battery to the 7 way, so you'll either need to run a new wire or trace the wiring on the plug to check for damage. Replace any damaged wiring you find.

If this plug was installed aftermarket, then you'll want to check to make sure that the fuse I mentioned above has been installed. The 30 amp fuse is installed in the power distribution box as shown in the photo I have edited. The power distribution box is located under the hood, on the drivers side on the fender well.

If that fuse is present or the wiring is completely in tact, let me know and I can give you a few other spots to check. I've also linked an FAQ article we put together specifically for a 1999-2006 GMC Sierra brake controller installation that you might find helpful.

expert reply by: Erik B

fuse location
(click to enlarge)

7 way plug diagram
(click to enlarge)

Mark

9/23/2024

Thanks for your help Eric. Mark here. Brake controller works fine. All the lights on the 7-way to the trailer are operable except the brake light power left and right turn signals work on the harness. Where does the brake lights come from? Pardon me the brake light power. I believe it's coming from the third brake light up high. Is that correct?

Mark A.

9/23/2024

Thank you, Eric! My brake controller works. I'm getting a signal for left and right turn signal. The only thing I'm not getting at my seven-way socket at the bumper is the signal or power to the brake lights? Also has this common in this generation GM? I have an issue with my map lights, my dome light and my cargo light. The third brake light works fine. Cargo light indicator on the dashboard comes on and stays on intermittently if the switch is on or off and I have no cargo light on