Recommended Trailer Wiring for 2016 Mercedes Benz 3500 Chassis Motorhome

Question:

Hi - I have a MB Sprinter 3500-based motorhome cutaway cab, fiberglass coach body. And Ive been using this type of adapter for the LED lamp out bypass function successfully for a relocated license plate/running light feed. https://www.etrailer.com/Wiring/Tow-Ready/20142.html#/ Now I find out that the motorhome manufacturer didnt combine the separate brake and turn signal light functions into the 7-pole trailer connector at the bumper of the motorhome, and Ill need to use the RM-732 or equivalent to get the brake light function to work on a typical LED trailer lighting application. As is, only the turn signal/4-way flasher functions work on the output of the Tow-Ready adapter. My question is this - Does the RM-732 provide the equivalent of the Tow-Ready LED lamp out bypass function? If not, will I need to install the RM-732 on the output side of the Tow-Ready adapter? Thanks

asked by: Phil S

Expert Reply:

Something doesn't add up with the description you gave. I recommend using a circuit tester like # PTW2993 to test the 7-way functions at your 7-way trailer connector. If they didn't combine the stop lamp and turn signal functions at the 7-way then you would be missing either the blinkers or the stop lamp because there simply aren't enough pins for them to be separate and all accessible for the trailer use.

I've attached a diagram of the 7-way to assist with the function locations. If they really didn't combine the 7-way functions correctly I recommend using a different system than the Roadmaster Brite-Lite # RM-732 which would work but also would then require the adapter # 20142 as well. If they wired what they already did incorrectly at the trailer hitch, then I recommend using the Upgraded Heavy Duty ModuLite Circuit Protected Vehicle Wiring Harness with Installation Kit # C59496 to get your correct wiring functions for your relocated license plate and other features. This will allow you to cut off the 4-way and directly wire those connections to the 7-way.

This will let you utilize LED lights after that control module without any issues.

expert reply by: Jason S