I put a new overvoltage relay in my 1990 300E (140K)about 5K miles ago. Fuse looked fine. Symptoms were intermintant rough running engine (and not just at idle guys), and ABS light on. I looked at alot of threads here, made voltage measurements (ok), etc., but just was not sure that my problem was the relay. I was really thinking a vacuum problem related to the ABS system ($$$$$$). Finally, I found a thread where one of the real MB mechanics mentioned "thumping" the relay as a check. As soon as the ABS light came on again (with the corresponding rough running engine), I pulled off the road, popped the hood, and tapped the relay with the handle of a screwdriver. The problem cleared right up! Evidently the 10 year old relay had corroded contacts. Since replacement, the ABS light hasn't come on once.