Hi all,

Our trusty old '88 300SEL (that I bought 10 years ago that is now my moms car) has been amazingly trouble free over the last 10 years we have owned it, though she is starting to show her age. The other evening my dad drove it to the market across town... on his way back, the car turned off and everything went black - headlights and all as he was driving down the road. It was as if the car had no battery or any power going to anything - it shut down as if you turned off a switch with no warning. He had a passerby help him push it into the service station. He set there for a couple of minutes and the car started back and ran fine and he made it all the way home with no issues.

Now here is something I think that may have caused something to go wrong... earlier in the day my nephews home school teacher had called my dad and said his battery was dead and needed a boost because he had forgot and left his lights turned on for hours. My dad had taken the Mercedes (and foolishly left the car running) while he jumped off his Honda Civic.

I am wondering if perhaps he shorted something out and now a main relay is going bad or something? The car had a new alternator put on about 2 months ago, not sure if that could be giving any problems or not?

Anyone that has had this happen and know what it could be... ?? Any info appreciated. My mom is frightened to get out in it now, thinking it may happen again with her driving it.

Thanks.

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2004 Toyota Sequoia Limited 4wd
1991 Lincoln Town Car Executive
1991 Cadillac Sedan DeVille
1988 Mercedes 300SEL
1972 Chevrolet Caprice Kingswood Estate 9-passenger wagon
1973 Pontiac Grand Ville
(Prior MB's: 1974 240D, 1985 380SE, 1984 190D, 1993 400SEL)

If your Dad just connected the jumper cables straight across to the poles of dead battery he could have caused a problem with the OVP relay. It's a less than $15 replacement. As you may know, the proper way is to jump a car is to connect the positive poles with one jumper cable, but use the other cable to connect the negative pole of the dead battery to a grounded piece of unpainted metal in your dad's car away from the battery. Your dad's car should be running so that there will be more than enough charge on the hook up to charge the dead battery enough to start the car (provided the dead battery can still hold a charge and is not too dead to revive).

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03 CLK430 Cabrio 211K Pweter Silver/ Oyster Leather
90 300SEL 214k Pearl Black/ Alto Grey/Black Leather

Prior: 85 190E, 88 300TE, 89 300TE, 90 300E 2.6, 90 300TE, 92 300E 2.6, 91 and 93 300SL, 87 Ferrari Mondial Cabrio

If the car restarted afterwards, the alternator, nor the battery are your problem.

If the headlights died as well, the OVP is not your issue either (their function is not tied into anything the OVP protects).

Most likely you either have a loose connection on the battery posts from the jumpstart (once load is applied and they heat up, they can lose connection) or you have a bad ground strap somewhere. I'd start by checking the terminals on the battery for tightness, then move to check the ground straps on both ends. Both the one that connects the battery to the body, and the one that connects the engine/transmission to the body.

Losing ALL electrical power like that indicates a total disconnect of electrical power (just like a switch as you mentioned). The alternator and OVP are highly unlikely to be your issues here.

__________________
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!)

Thanks so much for the replies.

As far as the way the battery was being connected during the boost, I am not sure how he hooked it up, I will ask him later.

Yes, he said the entire car went dead... the engine stalled instantly and everything went black - no warnings at all. It was as if the car was turned off and didnt have a battery at all. He let it set for a minute after he got it pushed off of the road and it started right up and drove fine the additional 7 miles home. I will check the cables later and see if I see anything obvious. It just sounds like some relay to me going bad or something, but I am not too sure.

Mom is wanting an SUV now as they are raising my special needs nephew and he is 8 years old now and they are needing something with more cargo room as he has a rather large stroller. Mom is also wanting something "more reliable" as this car is pushing 30 years old, but this car has never give me any problems when I would drive it and I still drive the car a lot when mom will ask me to take her somewhere. It has quit three times on my dad... once when the coil went out (twice), again when the alternator went out and then the other night, I am thinking it does not like him. lol. I believe that he thinks he is going to sell it when/if he gets mom an SUV, but little does he know, I want it back... I had looked for a 88-91 300SEL for years and finally found this one in 2007 and had her drove in 6 hours away. I never wanted to let it go, but mom needed a car back in 2010 and had asked me to sell it to them. I will take care of the MB if I get her back... I have 5 cars now, don't need another, but hate to see her go.

Thanks again!!

Connecting the negative lead last and away from the battery is a safety procedure in case hydrogen gases are present that could be ignited from the spark. I don't think that there is an electrical reason for doing it that way.

Check voltage regulator

Thanks!

Is there a way to "check" the voltage regulator on these, or should we just replace it? Also dumb question, where is it located on a '88 300SEL? I drove the car the other evening... started out of a parking lot. I noticed the radio had went off, came back on then the car went black (car turned off, headlights went off, everything). It was black for a moment, then I was able to restart it and come home. We need this fixed now.

Thanks!

To jump from good battery:

Positive to positive.
Negative to ground. Ground on the dead car; not the car doing the jump.

Just replace it, it's cheap ($20-50) and easy to do.

Pelican Parts - European Automotive Parts and Accessories - Porsche • BMW • Mercedes • Volkswagen • Audi • Saab • Volvo • MINI

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1979 Black on Black, 300CD (sold), 1990 Black 300SE, Silver 1989 Volvo 780, 1988 300CE (vanished by the hands of a girlfriend), 1992 300CE (Rescue).

Thanks!

Now just have to figure out where on the car it is. Time to go give it a good look over I guess. I read somewhere that it is built into the alternator on this car, but the alternator is barely 5 weeks old.

5 years, that's not much, how many miles? I'm pretty sure mine had still the original with 85K miles. I would check all the grounds as well.

The alternator is on the passenger side of the engine and the voltage regulator is on the back of the alternator, two screws hold it in place. Just follow the belt to find the alternator.

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1979 Black on Black, 300CD (sold), 1990 Black 300SE, Silver 1989 Volvo 780, 1988 300CE (vanished by the hands of a girlfriend), 1992 300CE (Rescue).

It is actually 5 weeks old (alternator that is). My dad had to replace it when the battery light came on and the car kept trying to stall. He had the alternator tested and they said it was bad, so he purchased a new Bosch alternator for it. It ran fine until he boosted that car off that day, then it quit that night. When it does it, there are no warnings except it seems the radio will go off and back on, then the car shuts down and all of the electrical turns off. It will usually start right back up after everything turns back on... sometimes its a few seconds, sometimes a few minutes.

Then your voltage regular must be 5 weeks old as well. It's my experience that when the voltage regular go's out, weird things happen in the dash cluster, like lights start to blink. I would check every ground and cable first and then go to a parts supplier like Auto zone and have them re check the alternator just to be sure it's not a faulty one. They do it for free.

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1979 Black on Black, 300CD (sold), 1990 Black 300SE, Silver 1989 Volvo 780, 1988 300CE (vanished by the hands of a girlfriend), 1992 300CE (Rescue).

This is not an alternator issue. If the entire car goes "black" and stalls out, but you can restart it after a few minutes of resting, you have a bad MAIN battery connection somewhere, or a battery that's bad. PERIOD. I'd start checking ground straps NOW. Don't waste your time with the alternator at this point, even if it's bad, it isn't what's causing your issues.

If the battery dies, it's dead. Resting isn't going to restart the car.

__________________
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!)

Thanks. I will look at some of the connections tomorrow. I am not much of a mechanic and my dad is a disabled veteran and cannot do much like he used to, so we will probably have to end up taking it to a mechanic. It was just odd that all of this started after he boosted that car off, but he told me it did that before (after telling me it didn't do it until after he boosted off my nephews school teacher), I don't know, I am not sure what he thinks sometimes, lol.

The car starts fine when it is cranking, not sure how it could be a bad battery, I guess anything is possible. It is a Mercedes brand battery that is at least 9 years old because I bought the car in October 2007 and it was on there when I bought it and we have never replaced it because it has never shown signs that it was going bad, I was thinking this issue it is having now was something totally different, but it may be the battery.

I have just never seen anything like that happen before... first the radio seems to go off and back on, then the car shuts off and it goes dead like it does not even have a battery on it - I mean all of the lights go off, headlights, dash lights, radio, etc. The night I was driving it and it did that, everything came back on after about 10 seconds and the car started right back up and I drove home the 30 minute drive with no issues. The time it did it to my dad, he had to let it set for about 10 minutes before everything came back on and was able to start it and drive on home.

My mom is to the point where she does not want to drive the car anymore because she cannot trust it and wanting to get a new car. I would hate to see this old MB go, she has been a good one, but may be time to move on. It has hard to find anyone around here that will even touch an old Mercedes as far as mechanics. I may end up buying it back from them like I need another car with 5 already in my fleet.

Thanks.