RV Doctor – My Tow Car Lights Don’t Work with my Motorhome

Tech Tips, Repairs, & Maintenance

March 31, 2010

123

March 31, 2010

Dear Gary,
I have a 1999, 37-foot motorhome. It has a six pin connector for the tow vehicle. My tow car is a 1995 Geo Tracker. The Tracker has different bulbs for brake and turn signal. The car was towed by the previous owner with all the lights working. I cannot get my lights on the car to work with my motorhome. The wire colors on the car are brown, yellow, green and white. I ran a diode between the brake light and the green and yellow wires on towed car. Still no lights, I can however, get the lights to work by running another ground wire from my RV hitch receiver to the tow plate on the car. What concerns me with this is that with the coach lights on I get a spark on the extra ground wire when I hook it up or move it. What am I doing wrong? – Joe DeRado, (Port Charlotte, FL)

Answer:

Joe, because you have independent stop and turn signal bulbs you definitely need that diode kit. And I suspect that you have already found the problem. It is likely that a ground wire is broken somewhere and therefore the circuit cannot find a decent path to ground.

The reason the extra ground wire is sparking is because the coach lights are on and the current is trying to flow to the tow vehicle lights. As soon as that ground wire is connected, the current is finding its ground path thus causing the spark.

You should find that if the lights are off and the ground wire then connected, no spark occurs. You would also get a spark if you were short circuiting the wiring, but this would result in a blown fuse and no lights operating. In fact it could blow the coach fuse as well.

To properly fix the problem I would begin by carefully inspecting the connector plugs. You can rule out the towed vehicle wiring as the cause since you obviously didn’t have a problem with the car by itself; neither did the previous owner.

The two most likely causes are faulty connections at the ground pins on the plug or receptacle or the motorhome frame ground. Keep the plug and receptacle free of dirt, rust, corrosion, etc. Also make sure the pins on the receptacle make good contact with the mating plug.

It is possible that the motorhome frame ground wire is either broken, damaged, or dirty and no longer making good contact. This is fairly common and can be easily remedied. Wire brush or sand the frame area clean, and then, using a new self-tapping sheet metal screw and a star washer installed between the frame and the ring terminal, secure a new connection to the clean vehicle frame. If it still does not work correctly, run a new ground wire from the plug connector to the motorhome frame as described above.

(Please feel free to comment, however, please also note that due to the volume of communications I receive from multiple channels I cannot guarantee a personal response in every instance. However, questions of an overall general interest may be considered and published in an upcoming RV Doctor column.)