How to Find COLD Side of Brake Light Switch for Hardwiring Brake Controller

Question

Question:

How do i get a hot wire off of brake light switch

asked by: Dave

0

Expert Reply:

When you are hardwiring a trailer brake controller like the Prodigy P2 # 90885 the red wire connection that provides the triggering signal to the controller should be made to the wire on the COLD SIDE of the brake light switch circuit. This is the wire that carries 12V power ONLY when you press the brake pedal and at no other time. Please refer to the linked photo and article for more details.

If you were to connect the Prodigy to the HOT side wire then the controller would constantly generate brake output to the trailer and you would not get too far.

Applying a circuit tester like # PTW2992 is the best method for finding the correct wire at the brake light switch.

expert reply by: Adam R

0

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Dan S.

3/30/2020

Tekonsha says not to connect to a wire that goes to ground when the brake pedal is not depressed. I have 2 wires in my brake position switch that get 12v when brake pedal is pushed, but they both go to ground when it is released.Any thoughts?

Chris R.

4/1/2020

You might be able to access the cold side of the brake light switch somewhere else on the vehicle (you're right not to use either of the two wires you found). If you can tell me what model vehicle you have I'd be happy to provide a more specific answer. Another option is to add a Brake Light Switch - which again are vehicle specific.

Frank G.

6/29/2022

@ChrisR I have the same problem finding a brake voltage that does not go to ground when pedal is not pressed. I have a 2011 Ford Ranger a d I’m pulling my hair out on this one. Where else could brake 12v be found in the cab ?

David B.

7/5/2022

Maybe this will help it is our video of a P2 install on a 2011 Ranger. https://www.youtube.com/watch?v=_qBVufIGQHI

See All (7) Replies to Dan S. ∨

Dan S.

4/1/2020

2016 Thor ACE motorhome built on F53 chassis.Every one Ive talked to and everything Ive read online insists that I have a plug and play connector in the dashboard. However, after removing the dash and searching through it, theres nothing even resembling one. There are several unconnected wires, but they have labels for PTO and blower motors. Not sure what you mean by Brake Light Switch, do you mean the switch thats activated by the pedal? Those are the wires Im referring to. There are 4: one is constant 12v, one is constant ground, the other two are the ones mentioned above. Where else on the vehicle could I access the cold side?

Chris R.

4/1/2020

Thanks for the info! It's really odd that it doesn't have a factory port - take a look at the linked answer below that actually shows a picture of its typical location so you can check one last time. If you still aren't able to find it, your best option is to use the Stop Light Switch Kit # RM-751000, which basically lets you wire in your own brake light switch to use for the controller.

Helpful Links

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Adrian S.

5/30/2025

I have 2003 gmc trying to wire and connect a Tekonsha red wire to cold side of brake switch what wire is the correct one

Robin H.

5/31/2025

@AdrianS a 2003 GMC what? I might be able to find the wire color if Roadmaster lists it but I will need to know the model of your vehicle. If they don't have the wire color you need to follow the instructions above and test to find it.

Answer 1

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Answer 2

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Answer 4

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How to Find COLD Side of Brake Light Switch for Hardwiring Brake Controller

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