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Trailer Lights Work But Brakes are Not Working


Have a trailer that have lights but no brakes. Hooked up to couple other trucks and still no breaks. Just wondering where to start


Expert Reply:

If you have a 7-Way on both your trailer and tow vehicle you will first want to make sure that you have a brake controller, like the Tekonsha Prodigy P3 # 90195. A brake controller is what is used to send power from the tow vehicle and tells the trailer how much braking power is needed. If you do not have one, just let me know what the year/make/model is of your tow vehicle and I will be happy to help you make sure you have the correct equipment.

If you do already have a brake controller then you will want to make sure that both the 7-Way on your tow vehicle and your trailer are fully functioning. Start off by looking for any corrosion build-up that could be causing the issue and clean it.

To test the functions of the 7-Way on your tow vehicle you can use a Circuit Tester # PTW2979 and test each pin as you have a helper inside the vehicle go through the functions. To test the brakes you will want to set the brake controller to the highest setting and send power to the 7-Way by using the manual override. This should send 12V power to the pin on the 7-Way that activates the trailer brakes. On the tow vehicle end this should be the pin in the 5 O'clock position (see attached photo).

If the 7-Way connector on your 7-Way doesn't get 12V power when the manual override is used then you will want to sever the brake controller wire, that goes to the 7-Way, about 6 inches away from the brake controller itself. If that wire is still not getting power when the manual override is used (and you brake controller is wired correctly) then you will need to replace your brake controller.

To test the brakes on your trailer you will want to use a 12V power source, like the battery on your tow vehicle, and test the pins on your trailer side 7-Way. You will want to especially pay attention to the pin in the 7 O'clock position (which is opposite of your tow vehicle) since that is the pin that should be activating the brakes. When you apply the 12V of power your brakes should activate and you will hear a quiet humming.

If the 7-Way on your tow vehicle is working correctly but when you apply the 12V power to the pin for the brakes on your trailer an it isn't working then you will want to check the wiring on your trailer. Look for any places where the wiring might be exposed, corroded, bent, or damaged and replace it. For the brake wiring you will want to use 10 Gauge Wire # 10-1-1 and Butt Connectors # DW05745-5.

If the connectors are working correctly and the wiring looks good but you are still experiencing issues then you will want to take your setup to a qualified mechanic who can physically inspect the wiring.

expert reply by:
Jon G

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