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No Electrical Power to Brake Controller

Tiny
HOOTACAROOTA
  • MEMBER
  • 2001 GMC SIERRA
  • 120,000 MILES
The brake controller on my 2001 GMC Sierra works fine with the manual control lever but not when the brake pedal is applied. The controller has four wires. Of the four, the red wire is supposed to receive power when the brake pedal is applied. However, there is no power at the red wire when the pedal is applied.

Everything else works fine. All of the lights on both the truck and trailer work as they should. I have replaced the brake light switch at the pedal but that did not solve the problem.

The brake light switch has six wires coming from it in these colors: Wt (grnd), Or (hot), Prp, Brn, Grn, Grn/Wt. None of the wires (except the orange wire) produce voltage when the brake pedal is applied. All of the wires (except the white ground wire) are hot when the ignition is turned on.

My questions are these: From where does the red wire on the brake controller get its power? How can I determine where the problem lies and how to fix it? Where can I find a high resolution wiring diagram?

Thanks.
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Monday, March 3rd, 2014 AT 3:32 PM

11 Replies

Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
According to our diagram there are only 4 wires going to the brake light switch and that is with cruise control as the other one has only two. The diagram that I've attached. I am assuming this is a 5.3L engine and has no traction control. Hopefully you have checked the fuses underhood for this. The red wire to your controller should go to the white wire so it powers when the brake is applied. However as this is an after market thing I would send you to a place that installs these andsee where they put it as it may be a wire that is supposed to be hot all the time and may be installed on the fuse box underhood. Isee no grn/wht wire on the diagram.
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Monday, March 3rd, 2014 AT 4:11 PM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Please note there is also a vehicle stop fuse underhood as well that is not shown. It shold be marked on underhood fuse box cover
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Monday, March 3rd, 2014 AT 4:14 PM
Tiny
HOOTACAROOTA
  • MEMBER
  • 5 POSTS
Thanks for the diagram. The brake light switch I have definitely has six pins.

I have checked all of the fuses and they are good. There is an additional, 30A maxifuse that is in Stud #2 in the underhood fuse box. This fuse apparently goes to the controller although it isn't identified as such on the fuse box diagram. Unfortunately, the 30A maxifuse is good :( If it wasn't, it might have fixed the problem.
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Monday, March 3rd, 2014 AT 5:12 PM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
No idea what to tell you other than previously as 2000-02 all show only 4 wires to switch but what I gave uyou is correct it may be a bad controller too.
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Tuesday, March 4th, 2014 AT 7:00 AM
Tiny
HOOTACAROOTA
  • MEMBER
  • 5 POSTS
Hmmmm. What I really need to find out at this point is where the stop light to brake controller signal is coming from. The controller isn't working when the brake pedal is applied because there's no power going to the red wire on the controller. The red wire gets its signal from the stop light which in turn activates the controller when the brake pedal is applied. What's confusing is that I can't identify how the brake lights are activated and how that signal travels to the underdash plug.
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Tuesday, March 4th, 2014 AT 7:12 AM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Stop light to controller was given in first reply.
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Wednesday, March 5th, 2014 AT 6:40 AM
Tiny
HOOTACAROOTA
  • MEMBER
  • 5 POSTS
The problem is that there are 6 wires on the brake light switch and none of them activate when the brake pedal is pushed. The white wire on the switch is always hot. All of the fuses are good. If I can find a convenient wire that activates when the brake pedal is pushed, I am not averse to jumping it to the controller.
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Wednesday, March 5th, 2014 AT 7:26 AM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Here is a trailer circuit that the lt blue wire shold be hot when brake is applied. BUT in the normal circuit the WHITE wire is hot when brake applied from switch on brake pedal. Are you sure you have checked all the fuses underhood for this? As that is where they are. See pic. I really don't know what to tell you other than to have alocal guy look at this. As everything I've sent shold have those working.
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Wednesday, March 5th, 2014 AT 7:36 AM
Tiny
HOOTACAROOTA
  • MEMBER
  • 5 POSTS
Ahhhh. The white wire. Fixed! I tapped into it.

I had thought the white wire was always hot. I think when I tested it before, I was lying on my back and I may have been pressing against the pedal.

Thanks so much for staying with me on this.

-John
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Wednesday, March 5th, 2014 AT 11:58 AM
Tiny
GUEV77
  • MEMBER
  • 1 POST
I have a 2004 chevy same problem how did u fix the white wire
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Thursday, April 11th, 2019 AT 12:12 PM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Hi Guev77,

This was an older post so I doubt they will reply so hopefully I can interpret what was done.

Looks like the issue they were having was the trailer controller was not receiving the brake pedal input. So when the brake was pressed, the trailer controller would not apply the brakes because it didn't know that the brakes were pressed.

It appears they jumped the white wire which is actually the ground to their signal wire so that it would see when the brake was depressed.

In my opinion, I think this wiring diagram doesn't match what the member's vehicle was. The ground should not be hot when the brake is depressed. However, if this is what yours is doing then you can do the same thing. If you provide me the detail about what your vehicle is, I will be happy to look up the wiring diagram for you so you can test your circuits and ensure you have voltage where you should.

In short, they most likely had a wiring issue and just jumped to another source for brake input rather than fixing the wiring issue. I guess technically they did fix the wiring issue by just using another source. Clever.

Look forward to hearing from you. Kenny
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Monday, April 15th, 2019 AT 12:12 PM

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