Thought I'd update this thread. My electrical was wonky. As well as the brake lights and horn, the ABS lite was on all the time, then the Def, fan etc, started acting up. It turned out to be faulty wiring at the fusebox in the driver's kickbox. No more ABS light, can blast my horn, and Def works in the morning. Yipee! I'm going to bake my mechanics some cookies
