I cannot find the thread but when last I posted I had a shifting problem due to a shop sending a rookie out to pressure wash the engine bay to get rid of the fuel smell resulting from a leaking injector hardline. Found my old mechanic and he found a small leak near the ALDA. Shifting problem gone.

Now I have a problem with a constantly on ABS light. This started with the light being on intermittently. I noticed when the light was on the tach stopped working and idle gets rough. Now that the light is on all of the time, I get both of those symptoms as well. Just changed alternator,belt, spring tensioner and dampener. The ABS symptoms were there prior to these changes.

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87 300D 265Kmi
Factory rebuilt crate 603.96x engine at 200K

OVP relay. Don't bother trying to fix the relay, just replace. Avoid the cheap brands, they aren't made well.

^^^^^ x2 on my '86 603 (including the cheap brand wisdom warning)

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1986 300SDL 440,xxx

OVP relay x2. When it fails or dies, your tach stops working because the EDS computer shuts down. The lack of idle correction speed results in a curb idle around 500 RPM and drops if the A/C compressor kicks on. The engine doesn't want to idle that low, so it is rough. ABS is also powered by the OVP. OVP dies, the light comes on. You may also notice some of your idiot lights are out when you turn the key before starting too. As said above, don't waste your time with repairs or 2nd hand parts. Buy new, buy OEM and be done with it.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Based upon the interaction with the tach and the EDS subsystem which controls idle speed, this sounds like the part to change. I seem to recall that it is behind the battery and is fairly easy to change. Correct? Final question: what are the cheapo brands? This site only offers one brand and the brand name seems to be URO-ish. Dealer item?

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87 300D 265Kmi
Factory rebuilt crate 603.96x engine at 200K

The bad ones are the no name brands on EBay. OE always works, and I've had good luck with KAE.

My first new KAE was no good out of the box. Second one has been working fine for 3-4 years (80,000 mi). I'd recommend the MB OE unit.

Maybe check the fuse in the existing OVP top before buying a new OVP. Also there is a fuse in the fuse box (see fuse box lid reference index for tach / fuse #) that when "iffy", will exhibit similar symptoms.

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1986 300SDL 440,xxx

If the fuse is blown, assume the unit is non functional. Even if it seems to work with a new fuse, the essential overvoltage spike protection cant be verified.

I would like to bet its still the same affer ovp swop .
But no news is good news ..

Idle is normal and no ABS light. Thanks to all who responded particularly Mxfrank. Got one from the dealer. Found that the OVP relay fuse was loose in the old one. I put the new one in and put the old one on the shelf since it is possibly still good. Thanks again. I never would have traced it back to the OVP.

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87 300D 265Kmi
Factory rebuilt crate 603.96x engine at 200K