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Old 05-18-2001, 06:27 AM
kfuller kfuller is offline
Registered User
Join Date: Dec 2000
Location: Montgomery, Alabama USA
Posts: 61
Overvoltage Relay

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.

Ken Fuller
1990 300E
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