PeachParts Mercedes-Benz Forum - View Single Post

JamesDean · #11 01-30-2015, 09:34 PM

Quote:

Originally Posted by yuke

On my 85 300 sd the problem was the ovp relay which is located in fuse box engine bay drivers side. Even though the fuse on top was good relay was bad. Not sure how to check relay one way would be to plug it in at a known spot that has current and see if it clicks or not. Some people shake and rattle them and not sure if you hear it rattle that means if it is good or bad. I guess compare it to a known good one.

If you don't have a known good one or access to another car to test your OVP in you can try bypassing it so long as you know the alternator/battery are operating correctly and are not experiencing anything odd.

You'll want to pumper pins 30 and 87. That will apply power to whatever the relay was powering.

In later cars there were more 87's I think than just a single pin but this should be a quick enough test I would think.

If bypassing the OVP does nothing than either the problem is in the EGR unit or the tachometer.

I've done a good amount of worth with these tachometers. I'd be happy to test/rework a unit if so desired.