I've got a 2004 hitop, ext bed 2500 sprinter. Had a class III hitch and 7 way plug installed abt a year ago and have been towing a small pop-up without a brake controller. All worked fine. Just got a larger trailer and added the brake controller. Brakes work, no error msgs, but the trailer lights don't always work. Semi stopped me on the way home and said the lights were not working. Got home and tested them - seemed like everything worked except the right brake light. Friend stopped by the next day and looked for me. Both brake lights worked at first, but after using a blinker, neither worked, then one, then blinkers didn't work, then did, etc. Ground wires don't appear to be loose. Took sprinter back w/o trailer (didn't want to tow back 60 miles with no lights and I was sure the brake controller was the problem). Mechanic claims everything works fine, so must be in the trailer. Am I nuts, or did I see somewhere that brake controllers on Sprinters will sometimes cause this problem? Will be taking the trailer back this weekend, but would like to be able to steer them in the right direction. Any help would be appreciated.