Hi guys, I'm new to the forum, so would just like to start by saying thank you for the great resource on these cars!

Here's my issue:

1992 Mercedes 300E 3.0 2wd 145k. Car broke down this morning. Dim lights, dim dashboard, very slow wiper, dash warning lights abs/srs/bulbs came on then the car cut out. Tried to crank it...nothing. No electrical power. Two minutes later it cranked and started right up. A minute later same problem occurred. Two minutes later, started right up. Repeat this all day. Now, once the tow truck got me home, I looked into it as much as google would let me (a lot), and everything pointed towards a bad alternator and/or a bad Voltage Regulator. So I changed the alternator for a new one. Started right up and ran perfect, idled for a good ten minutes no problems. Went to reverse it out of my garage, on came the warning lights and she cut out again. Now I am stumped. There's a relay that protects the system from voltage overload - I checked that and its own fuse which was good. Battery leads are all as new, battery is good, what the heck is wrong with my car?

I need help so badly, this is my daily and I had to take an unpaid day off today for the alternator which didn't cure the issue. Also, I searched as much as I could on this subject but couldn't find much, so apologies if the search engine didn't do its job.

Thanks guys I hope someone has some words of wisdom. Cheers!

These thing do come from time to time .The problem could be a host of things that can make your engine stop .Just one thing ,can you see the charging light as you switch your car on ? No need to start it up So.if you have no alternator llight, it may be the bulb in the circuit is blown .The battery wont charge up if the bullbs no good .I would also get the battery checked , it should show at its best 14 volts. Put digi meter on the + of battery and the - to a good earth on body tell us the reading .

Then after checking alternator , replace the overvoltage relay, you have more than 1 problem, the relay can cause most of it!

Thank you guys for your replies. I have a brand new battery on another vehicle which I am going to switch over to the Benz today and see what happens there. I will order a new ovr as well.

Classic worn brushes symptom, brushes wear to lose contact, no alternator light and no charge.

The regulator is an easy fix (with brushes).

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Gone to the dark side

- Jeff

Ok lets dismiss a few things first. The OVP protects computerized equipment, when it goes it affects the ECU, ABS, and a few other systems. But not the lights or wipers. The only valid test for an OVP is substituting a good OVP, I dont care what it says in the FSM or in misleading internet chatter. Second, if the alternator has been replaced withnew, the odds of having bad brushes is small. I think this is being caused by a bad main ground strap or loose battery cable.

Yep, missed that new alternator thing.

__________________

Gone to the dark side

- Jeff

I agree with mxfrank. You've already spent money which didn't cure the problem. So stop buying parts and start looking for the problem. If you think you've narrowed it down then test the alleged problem first instead of replacing the part. It could be a bad ground. Put the + probe of the multimeter on the + terminal, ground the other probe to the chassis and crank the engine. Should be idling at about ~13v - ~14.4v. If it's not then check the ground by the alternator to the negative block, check the belt tension, etc. Check all connections going to the alternator and going from (distributor block). Chances are it's going to be a loose cable. Welcome to the forum.

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1990 190E 3.0L

Thank you everyone for your comments. I appreciate that I can take your opinions/experience on-board and make the more logical approach instead of dribbling onto my hood.

As I said, I switched my alternator out for a new one. I managed through pure luck to get a killer deal on one, so I am not frustrated by that. Now I have a new alt. Then, after reading as much as I could about the OVP, I pulled it, cleaned it, changed the fuse, put it back in the car and while I still had a warranty on my battery I took it back and grabbed a new one. I also replaced the ground strap as it did have a bit of a kink in it, being so short. As a precaution, NAPA have an OVP on its way for me.

The car now runs perfect.

Thank you everyone.

So what was the problem with it?

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1990 190E 3.0L

I'm betting the ground strap.

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80 280SL
85 300SD
87 300TD
92 300D 2.5 Turbo
92 300TE 4Matic

Sorry guys, not been online to update my progress, and again I thank you for your input, so here we go.

Same issue happened today, 5:30am on I-215 in Salt Lake City. With a new battery and alternator and about 40 miles under their belts, the dashboard did a light show - dim......bright......dim.....bright...... the abs and srs light came on, then off, then on, then off....then the engine stopped at 70mph, all the dash lights and instrument panel was barely illuminated. I coasted on the shoulder in N to the exit and somehow managed to park nicely in a gas station, by the luck of the traffic lights.

No electricity. Two mins later, started right up, one min later, died. Got a tow to work, borrowing the work truck right now.

My new OVP Relay is on its way to me, should be a few days.

So, as the gentleman Mxfrank mentioned, the OVP protects the computerized parts, hence why the srs and abs lights come on if its tripped, but this complete consumption of battery power is boggling me.

You guys mentioned a main ground strap - from the - battery terminal to the chassis? That's new. Is the one from the bellhousing to the body a possible culprit?

Optimusprime, the alternator bulb? On the dash, is a battery icon right?

I'm being patient with my car, and I appreciate that you guys are being patient with me.

Yes it is the charging light for the alternator. With the bulb blown it wont charge up the battery . Also how as the weather been in your neck of the woods? you might have water ingress on to some of the electrical items.

All earth contacts you can see , take the bolt off clean it up on the end , and put a spot of grease on then you can fix it back in place. Can you take the ovp relay out, and give it a shake, if it is that something may be loose in side it wants replacing. These can be repaired after opening it up. Only joints come away ,re soldier them back will make it work .The fuse on the top may have blown check that as well. If you have a new ovp on the way strip out the old one in the car and inspect it for bad joints.

Thank you. So how is the bulb replaced?