No Signal or Function on Trailer Harness on a 2007 Acura MDX  

Question:

Expert Reply:

As far as I can tell, one of two things has happened. Either the tow wiring fuse has blown or the Modulite box on the harness has burned up. A short on the trailer could cause either of these and both would lead to no signals at the connector. I will walk you through a process to diagnose which is the root of the problem.

Using a circuit tester, like part # PTW2993, go to the back of the vehicle where the harness is attached. Un-plug the trailer harness and check the pins on the vehicle connector. Match the colors on the harness pins to the pins on the vehicle connector. Red is brake light, green is passenger side turn, yellow is driver side turn, black is power, and brown is taillights. If these pins are not working, then the fuse for the tow harness circuit is blown. You will need to consult your vehicle owner manual to figure out where this fuse is. There may be a fuse block behind a panel or cover in the driver side foot box and there are probably 1 or 2 more fuse blocks inside the engine bay. Sometimes the back sides of fuse block covers have a diagram of which fuse does what.

If you have power at vehicle connector, but not at the 4-Pole trailer connector, then chances are the trailer caused a short than burned up the Modulite converter instead of letting the signal feed back into your vehicle circuits and do damage there. The way to test is to check to see if signal is coming into the Modulite from the vehicle side and if it is going out of the box on the trailer side. I have included a link to a video showing how to test a Modulite.

expert reply by: Patrick B

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