Brake Lights on Trailer and 2013 Mazda CX-5 Do Not Work with Trailer Wiring Harness C56011 Installed

Question:

Hey guys! I installed this and it works for the turn signals for both my CX-5 and the trailer attached but now my break lights and rear tail lights are out on my CX-5 and dont work on the trailer. Any idea of what I did wrong here? Or how I can fix it? I was pretty sure that I installed it just as shown in the installation video here... Thank you!

asked by: Tyler

Expert Reply:

No brake lights on your 2013 Mazda CX-5 or the trailer? We can't have that! The first thing to do is to test the trailer wiring harness # C56011 using a circuit tester such as # PTW2993 or a meter if you have one.

Basically, you will be testing the wires going into the converter box from the vehicle first. Have another person sit in the vehicle and operate the brake lights/pedal while you test the input wiring for the harness. If you do not get a brake signal when doing this test then it is possible that there is a bent or broken pin where the harness tees into the vehicle wiring or there is a blown stop light or CHMSL fuse.

If everything is working correctly on the input side, then test the wires coming out of the converter (the 4-Way end). If everything was fine going in but not on the output side, then there is a problem inside the converter, and it will need to be replaced.

Another possibility is that the added power consumption from the trailer is overloading the vehicle wiring which could lead to a blow fuse or the system just refusing to work with the trailer wiring harness. So, if all of the fuses are intact and the 4-Way end shows that everything is working (without the trailer attached) but stops working when the trailer is connected then that would be the likely problem.

To solve that issue, I highly recommend a powered wiring harness, # 118563. With a powered harness the trailer lights will draw most of their power from the vehicle battery rather than through the taillight wiring. This also helps protect the vehicle's electrical system. The other solution would be to replace all of the lights on the trailer with LED lights and even then, there is still added power draw on the system so switching out the lights may not work.