It sounds like you have found the soon to be infamous problem with the Curt Lighting Adapter FR uses to interface the coach rear lighting. The Curt unit is at the rear of your coach just in front of the rear bumper. The wiring for your 7-Pin trailer lighting and the LED tail lights lights runs in to the unit. It then interfaces to the M-B OEM wiring harness via the Fuse Panel under the drivers seat.
Did you drive in the rain in the last couple days? Getting it wet can cause the Curt to freak out. Do a search in the Solera and MBS Chassis forums on "Curt" and you will find a lot of info and pictures of the offending unit.
The "Driver Side Rear Light" is the big, round, outside light on your slide out.
2017 Sunseeker GTS 2800 QSF
TOAD: 2016 Ford Edge Titanium FWD