I have a turn signal/brake light issue when towing my 03 Discovery behind a Mercedes Sprinter based RV. The turn signal and brake signals operate OK on both vehicles when operated separately in the Sprinter. The (weird) symptoms appear when the turn signal & brake functions are applied simultaneously in the Sprinter. In the Discovery the turn signal flashes on the opposite side from that selected and the brake light flashes alternately with the turn signal on the Discovery. The system operated properly for 2 or 3 years. I have replaced the Kurt 2 to 3 wire convertor in the Discovery twice with the original brand unit and once with a different brand. I replaced the lighting control module in the Sprinter, which contains a 3 to 2 convertor. The Discovery when connected behind a Jeep Cherokee operates normally. I believe the problem is in the Discovery, probably a ground issue. I have run a 10 ga test wire from the negative terminals of the Sprinter and Discovery batteries, and performed seemingly countless other tests, all to no avail. In the unlikely event that anyone has seen this problem I would appreciate knowing what the resolution was, otherwise any ideas would be appreciated.