I've recently started having some very odd problems with my 1987 190D 2.5 turbo.
I'd replaced the alternator with a new one a couple of months ago, but within the last month, I've noticed that the headlights and dash lights dim whenever the car is idling.

I figure it's the alternator that needs a new voltage regulator so I'm getting that taken care of tomorrow.
However, last night I started the car and noticed it's idle is far lower than usual, also, my anti lock brake warning light came on and all my gauges went dead for several minutes.
After a couple of minutes the warning light and the gauges came back to life.

I've replaced the fuel filters a few days ago and the engine usually runs OK, but for some reason it's idle sounded really low and quite different from most days.
Could there maybe be some connection between my ongoing electrical problems and engine performance?
Would the malfunctioning alternator account for the dead gauges?

I got the battery checked out at a shop and they said it was good and in working order, but they said it was the wrong battery though (it cranks out 850 cca and is a truck battery so I don't know if it matters or not).

I checked the fuse box and everything looks good.
Is there maybe something else besides the alternator I should be checking on?

Does your car have an overvoltage protection relay?

Sixto
87 300D

I'm not sure what that is. Where would I find it on the 190D?

It's behind the battery, maybe shielded by a plastic sheet. There will be a couple of relays and ECU type boxes by it. It'll likely be a tall metal box with a square cross section. It'll have a clear plastic lid over one or two blade fuses. Check those fuses. The relay can go bad without blowing a fuse.

http://media.photobucket.com/image/ovp%20relay/andrew_culture/Mercedes_1991_230te_W124_OVP_relay-.jpg

Sixto
87 300D

I think I found it. I didn't even know all that stuff was back there behind the battery. I found what I think is the OVP, Do I just yank on it to get it out or is there a better way to remove the OVP? I tried yanking but it just pulls loose with the wires it's attached to and I can't get a really good grip on it since it's so tight in there

Remove the battery for better access.






.

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1985 300SD
1983 300D
1984 190D
2003 Volvo V70
2002 Honda Civic

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BTW, 850 CCA battery is great for these cars . Thats what i get when i ask for a battery at Autozone.

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What Would Rudolph Do?
1975 300D, 1975 240D, 1985 300SD, 1997 300D, 2005 E320 , 2006 Toyota Prius

Sounds normal. One characteristic of '80s and older Mercedes is their low charging output at idle, they have even designed in automatic shutoffs in the rear defogger and seat heaters if it drops too low, to help keep the battery from discharging (they flash, then turn back on when the voltage recovers).

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Gone to the dark side

- Jeff

Thanks for the advice. I"ll try to lift out the chunky battery tomorrow when there's daylight. I'm going to see how much the OVP relay is tomorrow at Lordco and also get my alternator fixed up while it's still under warranty. Hopefully I won't have to spend too much money on it since I also need to get a blower motor so I have window defoggers for winter.

Have you measured the voltage? You're driving without a roadmap if you haven't, the charge dropping at idle is normal, if you're idling too low because of a bad OVP/fuse, even more voltage drop.

Ever heard the phrase "measure twice, cut once"? You've already got the saw running, and haven't even opened the tape-measure.

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Gone to the dark side

- Jeff

The guy at the alternator shop said it was charging a bit low and my headlights seemed to dim even at normal idle before I noticed problems associated with the OVP relay which started last week. I probably should have been more thorough in checking out all the leads though. My car's at the shop right now so if everything checks out then I"m buying a new OVP relay and popping it in tomorrow.

Well, the cars back from the alternator shop, same problems as before. I finally got the OVP relay out, took me about 20 minutes of swearing and hard pulling. I have the thing here on my desk, I notice it's the original one and I can't seem to be able to take it apart. Everyone keeps talking about the "two tabs at the bottom" but I can't seem to find a way to get this thing apart without breaking something.

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I have taken apart and repaired 2 OVP relays. You will need to use a small screwdriver to VERY CAREFULLY pry the aluminum housing away from the base of the relay. This can be done without tearing the aluminum, but patience is your friend.

Once the outer housing is off, you will want to visually inspect the riveted connections at the base of the relay. Chances are good that corrosion has set in, and one or more of the pins is making an intermittent connection.

Clean the connections well, then break out a good strong soldering iron to repair the joint. Yes, it's a pain, but OVP relays aren't cheap.

I keep a back-up OVP in the spare parts box in my trunk.

Steve.

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'93 190E/D 2.5 Turbodiesel 5-speed (daily driver)
'87 190D 2.5 Turbo rustbucket - parts car
'84 Dodge Rampage diesel - Land Speed Record Holder
'13 Ram 2500 Diesel
'05 Toyota 4Runner

Personally, I'd just buy a new one, and if the old one can be repaired it will make a good spare.

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Gone to the dark side

- Jeff

Success! Well, went out to the Mercedes Service depot and got myself a new OVP relay yesterday. I took the battery out and installed it and now everything works. Only cost me $7 more than what the junkyard wanted for one. Now onto the blower motor......