Trailer light issues - On the bus

[Turbine Bob]

I am out of ideas, so I thought I would try the forum. I have a 2003 Fleetwood Providence, Freightliner chassis. What is happening, I believe has been an issue for a long time. My tail lights, signal lights and stop lights on the bus work fine as long as I don't hook up my Mini. (Note, I hooked up the Mini to my GMC pickup that has the same lighting scheme with separate turn lights and it works just fine.) I started troubleshooting and after several hours (even called Fleetwood) I determined that when the brake is depressed, the voltage output at the trailer connection for the Left and Right side stop/turn lights reverse polarity! That is the ground wire becomes 12 VDC positive and you read negative 12 volts between the trailer wiring connections and ground. (Oh yea, the turn lights work fine as do the tail lights...just the brake.) Of course if it is hooked up to the car, that is a direct ground and it immediately blows the stop light 20 amp fuse.
I checked the wiring as far as I can, pulled the relay block cleaned it and checked each relay with an ohm meter. No problems. I checked the output from the brake relay when the brake pedal is depressed is positive 12 VDC referenced to chassis ground going into the wiring harness and the ground wire that is daisy chained to all 4 relays.
I am pretty much stumped. I do know that some where in the wiring harness they spliced the wires as the ones in the relay and fuse area are much smaller gauge than the wiring at the trailer plug.
I even cut off each wire at the trailer plug and verified that they were connected properly and there were no loose wires.
Has anyone had this problem. Fleetwood said that there was a connector in front of the drivers side rear wheel, but I cannot find anything. All of the wiring in that area is tidy and no sign of a connection.
If anyone has any trouble shooting ideas, I will certainly try them. I have given up trying to correct the problem and tomorrow I am going to buy a converter system that goes from the 4 wire input to a 3 wire output and hook them directly to the lights on the rear. Note that the voltage does not change polarity at the rear brake lights. Any ideas!!!
Thanks
Bob Doughty

[dvmweb]

So, it never worked correctly with your mh and the mini? Would a short or bad ground somewhere reverse the polarity? Or, is this normal? Are there any diodes involved, in the mini especially?

We towed a Jeep Liberty for a while and a diode for the toad lights failed and would blow a tail light fuse once in awhile. In future we will use add on external lights.


2013 FleetWood Expedition 38B