How Do I Test My Curt Spectrum Brake Controller to See if the Module Is Bad?

Updated 08/27/2026 | Published 08/20/2026

Question:

i purchased a curt spectrum brake controller for my 2006 hummer h2. it came with the adapter to plug it into the truck. i hooked everything up and im not getting any power to the controller. i went to a trailer lot and had them look at it. he tested the plug in at the bumper and also checked the fuse. everything worked properly. he said it may be the brake controller module that is bad. is there a way to check it to see if that is the case? or can i get a replacement for the one i have?

asked by: Lee G

Expert Reply:

Hello Lee,

Thanks for writing in, I am sorry you are dealing with this headache.

It sounds like the trailer shop already helped rule out a few things, but before we call your Curt Spectrum # C24SV bad, I would check a couple more things.

The Spectrum is a proportional brake controller, so it needs to feel your Hummer slowing down to give you normal braking output when you press the brake pedal. If you are testing it while sitting still, try the manual override with the trailer connected. The manual override will apply the trailer brakes even when you are not moving.

If you are getting absolutely no lights or response from the controller, unplug it and use a circuit tester or multimeter to make sure you have 12V power and a good ground at the Curt harness where it plugs into the controller. If you have both and the Spectrum still will not power up, then I would say we have narrowed it down to the controller itself.

Let me know what you find out.

What kind of trailer are you towing with your Hummer?

expert reply by: Kate F

Lee G.

8/26/2026

It’s a 2023 ez-loader boat trailer. I also have a 2018 GMC sierra that I tow the same trailer with and have no issues. It has the factory brake controller setup. So I know it’s not a problem with the trailer.

Kate F.

8/26/2026

@LeeG Have you tried testing it with the manual override before? Usually that does the trick. If the controller is bad, we will definitely get you another one out and a label to get the defective one back. I have a surge brake actuator on my Ranger. The braking isn't as great as using a set-up with a controller, but it gets the job done.

Lee G.

8/26/2026

I have an appointment this Friday to take it into a shop and have them look at it. I’m not getting any power to the knob installed on the dash. When I first hooked it up there were two blue lights on either side of the knob and that was all. Now there is nothing. From what I understand the two blue lights indicate there is nothing trailer hooked up. When I had the trailer hooked up the blue lights were on. I will know more this weekend after my mechanic looks at it.

Kate F.

8/27/2026

@LeeG The fact that you had the two blue lights when you first installed the Curt Spectrum is helpful because that tells us the controller was getting power at that point. You are also correct that the blue lights indicate the controller is not detecting a trailer. Since you now have no lights at all, even with the trailer connected, having your mechanic check for 12V power and a good ground right at the controller harness is exactly where I would start. If both are good but the controller still will not light up or respond, then we have done a pretty good job narrowing it down to the controller itself. Yes, please keep me informed, I will make sure you are taken care of.