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

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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?

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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.

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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 ?

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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

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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?

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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

question-311209.html

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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

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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.

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Answer 1

Normally you can find the brake light switch under the dashboard at the top of the brake pedal. There could be a number of wires attached to the switch so you can use a tester like part #PTW2993 to test the wires. Since the auto manufacturers can use…

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Answer 2

I would be happy to help you set up your 2021 Chevrolet Spark for flat towing. First and foremost your Spark can not be flat towed if it has an automatic transmission. If you do have a manual transmission, here are the parts you will need to flat…

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Answer 3

You do have the option to utilize the air brakes on your 2023 Freightliner Cascadia to control electric trailer brakes using the Hayes Air Actuated Trailer Brake Controller, part #HA100400C. However, we mostly recommend just using an electric brake…

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Answer 4

For your 2020 Kia Telluride you need to start off with the T-Connector Wiring #CU94FR which plugs into a connector under your vehicle on the driver's side. Then for a brake controller I highly recommend using the Curt Echo #C51180 because you…

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Answer 5

A 4-Way trailer connector has the basic lighting functions only; running lights, left turn signal and brake lights, right turn signal and brake lights, and ground. A 7-Way has these functions and a 12 volt circuit, a circuit for electric trailer…

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Answer 6

From my research your 2017 Jeep Wrangler Unlimited should already have all of the fuses and relays it needs to tow a trailer. You can check your owner's manual and verify the fuses to be absolutely sure. Whether it is equipped for an electric…

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Answer 7

I checked with Roadmaster to confirm but yes, you can use the Roadmaster Battery Charge Line Kit for Towed Vehicles item #RM-156-25 on your Hybrid 2023 Ford Maverick. Some other parts you will need to flat tow your Maverick are listed below. Please…

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Answer 8

There aren't as many custom fit flat towing wiring harnesses for vehicles like there is for trailer wiring so what that means is that for your 2023 Ford Maverick there are only kits that require wiring like the Roadmaster diode kit part…

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Answer 9

For hardwiring a brake controller in to a vehicle like your semi you would want to check out the help article I attached that details how to hardwire a brake controller. I attached install instructions for the #90885 as well, but the help article…

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Answer 10

To work with your electric over hydraulic actuator, you would set your Tekonsha P3 to electric over hydraulic mode, by pressing the menu/options button. Then, on the SETUP screen, scroll down to brake type and press OK when Hydraulic is highlighted.…

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Answer 11

The trailer brakes work on a separate circuit than the lights. You have a couple of options to control the electric brakes on the trailer. One option is to use an air over electric brake control, #HA100400C. This unit connects to the air brakes on…

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Answer 12

You certainly can! Installing a brake controller is fairly easy if you are familiar with running wiring. To install a brake controller like the popular Tekonsha Prodigy P3 #90195 you will need to run the wires on the pigtail to the following…

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

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