Rented Trailer Lights Not Working with Wiring Harness on 2006 Honda Odyssey but Work with Truck

Question:

Hitch and harness installed without problem. I used the spacer blocks and special cone washers. Bolts were torqued to specification using adjustable torque wrench. I tested the harness with multi-meter, Blinkers, running lights and brake light power as expected. When I connected the harness to a rented trailer, the lights did not work. Trailer worked when connected to a truck. My harness checked out fine. We used a jumper from a known ground point on the vehicle to ground the trailer. Lights started working. My hitch is not grounded even though it is bolted to the frame of my vehicle. The hitch itself, not just the receiver. Does the trailer have to be grounded through the connection with the hitch? I have not seen any Q and A topics regarding a grounding problem or additional grounding strap. Any recommendations?

asked by: Danny W

Expert Reply:

There is likely a ground problem on the trailer. Trailers that will only ground through the ball or otherwise coupled to the trailer have a ground issue that needs to be addressed. The other possible issue is that the trailer draws more power than what the wiring harness is rated for. If I knew the wiring harness you were using I could most likely determine what it is rated for.

To test this you can disconnect some of the lights. If everything starts working then the issue was the over-draw.

Make sure that the trailer connector on the trailer is clean and free of corrosion and that its ground is attached to a clean and corrosion free bare metal surface.

Not all wiring harnesses are created equal. The wiring on the truck may be able to either compensate for a weak ground or has the capacity to handle the power draw if that is indeed the case. It is not uncommon for this to happen. You will also want to make sure you have a good ground for the wiring harness on the vehicle. A painted surface will not work well and a location that already has grounds on it may not be the best place either.

expert reply by: Michael H