All Lights Work Except Brake Lights on Trailer Towed by 2013 Kenworth Class 8 Truck

Question:

All lights work except brake lights on both sides I have reason grounds at plug and lights it is hooked to 2013 kenworth any ideas greatly appreaciated

asked by: John

Expert Reply:

Class 8 trucks typically have a different set up 7-Way than passenger vehicles and that could be the issue. Disconnect the trailer from the tow vehicle and use a circuit tester, such as # PTW2992, to test the pins on the vehicle side connector. Have someone sit in the truck and step on the brake while you test the pins in the 3 o'clock and 9 o'clock positions.

If the brake pedal does not make the tester light up, then this is most likely the issue. Trailers that take a 7-Way blade style connector have combined turn signals and brake lights. The pin at 9 o'clock is left turn/brake and the pin at 3 o'clock is right turn/brake.

To get it to work you will need to combine the brake light signal with the turn signal wires. You can do this by using a special converter, # RM-732. On the input side, white is ground, red is brake light only, green is right turn only, and yellow is left turn only.

On the output side that will go to the 7-Way, green will then be combined right turn and brake lights and yellow will be combined left turn and brake lights.

expert reply by: Michael H