Troubleshooting Brake Controller Installation On 2003 GMC 3500

Question:

I Just received a new Curt Brake Control with wiring adaptor for my 2003 GMC 3500. I hooked up but the trailer plug in at rear of truck is a seven blade standard RV hookup. The Blade for brake reads 12.33 volts all time. With brakes activated reads 12.36. Plugged right in factory box. My other brake controller was doing same thing. I just purchase this truck when I noticed during checking back plug before towing it was also reading within a few 10ths. This is why I replaced it after checking with meter, factory plug under dash and wiring to back of truck. All wiring is cleanly done, the rear plug is a plastic one. Is this normal? Doesnt seem normal to me. I have checked and cleaned all respective parts. If I may provide any other info I will be glad to. I may be working out of town and slow to respond back but will as soon as I can. Thanks for any help you can provide.

asked by: Tommy A

Expert Reply:

When checking the brake output circuit of a 7-Way there should not be 12 volts of power all the time. A Curt brake controller will have what is termed 'dead' voltage at idle. This means there is voltage but no amperage draw. You can test for amperage instead of voltage to see if that is the case. If so, then you do not have a problem. If you are showing amperage draw that would indicate a short somewhere or possibly a problem with the brake controller. For a Curt brake controller, and if you have a factory 7-way, the correct adapter is part # C51352.

You will want to check the 7-way Since you said you recently added the 7-Way without the brake controller installed. You may find that the 12 volt circuit is somehow touching the brake output circuit inside the harness. That may be what is causing the constant power draw.

If you find it is working properly without the brake controller installed, it is likely a problem with the brake controller. To test the brake controller, sever the blue wire a few inches back from the rear of the controller. Then use your circuit tester to check the end coming out of the controller. It should only show power when you apply the manual override. If it shows power at any other time then there is something wrong inside the controller and it will need to be replaced.

I have included links to helpful articles for wiring and troubleshooting brake controllers you can check out.

expert reply by: Jeffrey L