Tail Light Wiring for the HHR in Tow Update

Well, after several troubleshooting sessions at the back of our RV, scratching my head, researching and reading about trailer wiring, towed vehicle wiring, I finally found the solution to the brake light issue on the magnatic tail lights for our HHR when it's being towed behind our Discovery.

It appears that previous owners had different tow vehicles that needed different brake controllers because there are two separate brake controllers mounted on either side of the steering wheel at the driver's console.  Here's what I found and the solution I came up with to get the brake lights to illuminate properly on the magnetic tow lights for the HHR.

1. There are two receptacles mounted under the back bumper, a 6-pin round and a 7-blade round plug style connector.  Since I don't need 7 wires to connect the magnetic lights, I chose to use the 6-pin receptacle and only use the 4 wires that came with the magnetic lights.
2. After numerous discussions with others on the Discovery Owners Forum and further research on the tail light wiring systems for big RV's like ours, these big rigs have separate circuits for brake lights and turn signal lights.  The turn signal lights are separate amber fixtures and the brake lights are a dual filament bulb combined with the running lights. and the wiring harness provided by the chassis manufacturer uses five wires:

• Chassis Ground
• Left Turn Light
• Right Turn Light
• Brake Lights
• Running Lights

Trailer lights are normally a four wire system:

• Chassis Ground
• Left Turn Light (brake)
• Right Turn Light (brake)
• Running Lights

In order to make a four wire tail light system work, there has to be a converter wired in between the five wire and four wire system that illuminates both tail lights (left turn and right turn) for proper brake light operation.  I found a tail light converter at Autozone and wired it in-line into the five wire harness going the the 6-pin receptacle on the back of the RV.

The four wires on the output side of the converter were wired into the appropriate pins on the receptacle as shown in the diagram here.  I cut the 4-wire flat connector that came with the magnetic lights and connected the four wires to a 6-pin plug to match the receptacle.

After all this reconfiguring and wiring modifications, I tested the running lights, turn signal lights and still had only one brake light showing on the magnetic tail lights. Hmmmm, I had to get out the 12volt test light and discovered that the red wire that was suppose to be the brake light didn't have any power at all when the brakes were applied.  I started probing the wires in the other wire bundle that went to the 7-blade receptacle and couldn't find any with 12volt power, and then it dawned on me that maybe one of those brake controllers up front had to be on.  After I turned on one of the brake controllers and set the sensitivity, one of the wires in the 7-blade bundle showed power when the brakes were applied, so I had to connect that wire to the red wire going into the converter, and voila, I had brake lights on the magnetic tail lights for the towed vehicle.  It may not be properly wired, but I did get them to work, so I'll have to trace the wiring harnesses back to see where the factory brake light wire originates and rewire it to the converter.  I really want to remove those brake controller units from the driver's console, they're an eyesore.  Here's the magnetic brake lights I am currently using: