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2017 GLS 550 trailer brake lights not working (not LED)
I searched this forum and did not find this particular trailer brake light issue - lots of discussion regarding LED trailer lights (which I don't have) and programming of the vehicle when the hitch is installed (which I believe was done correctly by the dealer - see below). Any assistance would be appreciated.
2017 GLS 550 (X166) with dealer installed Mercedes trailer hitch, installed two years ago. At the time the mechanic at dealer claimed that he tested the electrical installation with their trailer light tester and stated all was good.
Two years later and this is the first time I am using the vehicle for towing. Discovered that trailer brake lamps do not light when brake pedal pressed, but other trailer light functions work (turn signals, flashers, running lights). Trailer lights are incandescent, not LED. Validated that trailer lights are all working correctly (including brake lights) with different tow vehicle (Honda CRV).
Using CURT 57004 7 pin round to 4 / 5 pin flat LED electrical adapter (has built in resistors for trailer LED lamps). Also tested with Pollack 7 pin round to 4 pin flat adapter without resistors and same problem.
Vehicle recognizes that trailer is connected because I get the warning message “Act. Blind Spot Asst. Not Available When Towing a Trailer See Operators Manual”. Also error message in center of dash “Check Trailer Brake Lamp”.
10-18-2023, 02:45 PM
