Mercedes/Trailer Lights Compatibility Issue

Question

Hi all,&nbsp;I'm having a strange electrical issue and would be grateful for some advice.&nbsp;We recently purchased a used boat trailer and a 2020 Mercedes GLS 450 suv to tow it. The Mercedes has a 7-pin plug and the trailer light system is 4-pin. I bought a 4-pin to 7-pin adapter from Curt. With the adapter, the trailer lights come on, but only solid red. The turn, hazard and brake signal functions do not work.&nbsp;The trailer is pretty old and corroded, so I had the lights replaced with a new Kenway system from Harbor Freight. Same result, lights burn solid, won't signal. So to test the system I plugged the trailer into my Tesla's 7-pin plug, and everything worked correctly.&nbsp;We had a trip coming up in a few days, so in a desperate move, I bought a magnetic clip on trailer light system (also Kenway) and...everything works correctly with the Mercedes using the magnetic system. The magnetic lights got us through the trip, but taking them on and off during the launch/haulout is an extra step I'd be happy to skip if possible.&nbsp;So basically both the Mercedes and the trailer lights work correctly, they just don't work together. I'm assuming there is some kind of voltage/resistance compatibility issue between the Mercedes and the trailer, but don't really know where to start. If anyone has suggestions on what to try next, I'd appreciate it!&nbsp;Thanks,&nbsp;David&nbsp;

way2roll · Answer

Not sure what this has to do with RVs. Assuming you're coming here in case someone has a similar issue. I had the same problem with my Mercedes based motor home and LED wireless lights on our toad. Tow lights require a certain voltage. The Mercedes equipped with LEDs sends too little voltage to the trailer wiring harness and they don't behave as a result. Sounds like you need a resistor adapter. It will trick your trailer lights into getting the proper voltage to work. Worked in my case anyway.

optimistic · Answer

Yes, sorry, I was pushing the limits of "RV" with a boat trailer, thanks for replying.&nbsp; I did get an adapter from Curt that claimed to solve this issue but unfortunately did not.&nbsp; It DID make the difference on the temporary light system, as the initial 7-pin/4-pin adapter didn't even do that.&nbsp; Can I ask what adapter unit you had success with?&nbsp;

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Mercedes/Trailer Lights Compatibility Issue

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