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How To Find Cold Side Of Stop Light Switch On Vehicle For Brake Controller Installation  

Question:

Hi, where can I find the the cold side of brake switch to attach to the brake controller, what color is the wire and where is it located. Thanks

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Expert Reply:

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 different color wires it is always best to use a tester and check the wires for function and not color.

You would need to find the wire that only shows power when the brake pedal is pressed. That would be the wore that gets attached to the red wire from the brake controller.

If you want to let me know the year, make, and model of your vehicle I may be able to provide more information for you when installing a brake controller.

expert reply by:
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Jeffrey L

Aaron

5/10/2020

I have a reese brake controller, Brake-EVN proportional. I don't know where my cold side connection is on my 99 dodge ram 1500. To connect the red wire to the stop light switch.

Etrailer Expert

Chris R.

5/13/2020

To find the right wire, you'll just need to use a circuit tester on the wiring behind the brake pedal. You're looking for the wire that ONLY gets power when stepping on the brake pedal (and no power with any other function). Unfortunately I wasn't able to track down what color this wire might be on your 1999 Ram 1500.

What F.

9/20/2020

What if you have air barkes? (I have a 2004 Ford
Etrailer Expert

Jon G.

9/21/2020

@W I'm not super familiar with air brakes but from my understanding there should still be a cold brake light wire somewhere - you'll just have to use a circuit tester like what Jeff and Chris mentioned. If you absolutely cannot find one then installing something like the Roadmaster Universal Stop Light Switch Kit # RM-751000 might be your best solution.

Ed

5/14/2024

Trying to install a Roadmaster brake light relay in 2018 F150. I have two of four wires at brake light switch that give 12v when brake is depressed. Purple/white and purple/pink

Etrailer Expert

Mike L.

5/29/2024

@Ed You're wanting to use the purple/white wire.

Kee

6/12/2024

I have 1996 xj Jeep Cherokee. I need to find which wire is for cold side of brake light switch? There are several lines coming out of the switch. Which color is it for cold side of brake light switch?

Etrailer Expert

Bud M.

6/12/2024

@Kee I was able to find one source which said it is going to be a white wire with tan stripe. You should verify this using a test light on your particular 1996 Jeep Cherokee XJ to ensure it functions correctly when pressing the brake pedal.

Kee

6/12/2024

Thanks
Etrailer Expert

Bud M.

6/12/2024

@Kee You're welcome!

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