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  #1  
Old 01-11-2002, 01:03 AM
sixto's Avatar
smoke gets in your eyes
 
Join Date: Jun 2000
Location: SF Bay Area
Posts: 19,759
91 300SE electrical problems?

I posted earlier today that my speedo bounced a couple of times when I came to a stop and the windshield washer light came on yesterday. On my way home tonight, the speedo was fine and the windshield washer light was off (I haven't checked the reservoir). Then the ABS light came on... then the SRS light came on... then the ACC went to full heat... then the tach and speedo started bouncing... all the lights dimmed... finally the engine stalled. After checking all the fuses (even the OVP fuses) it restarted and seemed fine. After moving a few feet, all the electricals went crazy again and the engine stalled. I had it towed the rest of the way home.

BTW, the battery light does NOT light when I turn the key to on. But the factory radio or something in that area clicks like mad. And the radio turns on when I turn the key to on even if I turn it off before I take out the key.

I'm now off to archive and CD manual land. Any ideas or thoughts in the meantime would be most appreciated. "I have for sale a 300SD/L in white with grey interior in great condition" would really be music to my ears

Thanks,
Sixto
91 300SE ... what's going on?
81 300SD

Last edited by sixto; 01-11-2002 at 01:21 AM.
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  #2  
Old 01-11-2002, 03:10 PM
sixto's Avatar
smoke gets in your eyes
 
Join Date: Jun 2000
Location: SF Bay Area
Posts: 19,759
Did a couple more tests:

- battery at 11.6V with the engine off, 13.9V with the engine running. Doesn't vary much with load or rpm

- with key in on position before starting the engine, the brake, ABS, SRS and check engine lights come on. The ABS and SRS go off after a few seconds. The battery light glows dimly while cranking. The high beam, brake pads, oil level, coolant level and bulb lights don't come on with the key in this position.

Also, the radio keeps coming on on its own. Every time I start the car and even after I turn it off with the engine running. I mean the engine's running, the radio comes on, I turn it off, it comes on again... and again... and again.

Help!

Thanks,
Sixto
91 300SE
81 300SD
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  #3  
Old 01-11-2002, 05:00 PM
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Join Date: Jun 2000
Location: Plano, TX
Posts: 2,503
Could well be a dying battery. At 11.9 volts it's down a bit from where it should be. Since voltage comes up when running, charging system appears to be OK. You should be able to get both the battery and charging system tested for free at any McParts auto store.

My personal experience is that MBs can do strange things when the battery is on its last legs. My spouse killed the giant Diehard in her diesel wagon late last year by leaving the headlights on for several hours. Even after jumpstarting the car, many strange things happened. ABS and ASR lights on, A/C compressor engaged with the climate control in economy mode, even an occasional phantom windshield wiper stroke. Replacing the battery with a fresh one banished all the ghost problems. Strange but true.
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  #4  
Old 01-11-2002, 05:05 PM
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Join Date: Dec 2001
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Sixto:

Last night I resolved a problem on my '91 300-SEL that is similar to yours in some respects.

My wife came home the other day after a 30 mile drive back from the big city. The car stalled in front of the mail box. I went out to start it and saw an ABS/SRS/CHECK ENGINE light on while idling.
Got it in the garage and 1st checked the infamous OVP fuse. Looked good - VOM/Ohm check confirmed this.
I became suspicous and tested the battery with car off. It read 11.84 volts and that was on a fully-warmed up engine. I knew right away I had an electrical situation.

Searched the archives hear for ABS/SRS light on issues. Found numerous items. Most pointed to a faulty regulator brushes. Put the front end up on ramps and pulled the regulator out of the back of the alternator. Part number 1-197-311-023 is the
regulator. The outer brush was about 1/16" long; the inner brush was about 3/16" long. Bought a new regulator. The brushes in the new regulator are about 1/2" long. Installed regulator, reconnected battery cables(had to rechange battery some) and the ABS/SRS/CHECK ENGINE lights are now gone once started. When I first turn on the key, I now get the various dash lights. When I had only the ABS/SRS/CHECK ENGINE light, I would see none of the others light up with the ignition was first switched on.

Check your voltage regulator. It's worth a shot.
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Old 01-11-2002, 08:20 PM
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smoke gets in your eyes
 
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Thanks, Mike. I'll check the regulator brushes ASAP. Any tricks to working on the regulator or is it as easy as you make it sound?

Sixto
91 300SE
81 300SD
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  #6  
Old 01-11-2002, 09:46 PM
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Sixto:
Changing out the voltage regulator on a '91 300SEL is without a doubt one of the EASIEST tasks I've ever performed. If you have it in your hand and the car is already up on ramps, it might take you 3-4 mins. altogether. 2 phillips head screws come out and so does the volt. reg. The new one will have brushes about 1/2' long, so you will have to cant them a bit to get them in. No big deal. Even though you have no elect. connections to undo on the vol. reg.(at least I didn't), you might want to pull the battery grnd. strap first just for safety sake.
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Old 01-12-2002, 07:53 PM
sixto's Avatar
smoke gets in your eyes
 
Join Date: Jun 2000
Location: SF Bay Area
Posts: 19,759
I pulled the voltage regulator and found one clean brush and one carbon lined brush. Photos are available at photos.yahoo.com/tabijan in the MB Voltage Regulator album. Sorry about the quality, my camera doesn't take good close ups. I presume the problem stems from one brush not making contact with the armature (or whatever it contacts). I guess we'll find out when the replacement regulator gets here.

For the purpose of the archives, removing the regulator requires nothing more than a Philips screwdriver. I had to get to the alternator from below. Let's see how much fun it is to install the replacement regulator.

Thanks for all who offered help. It's all much appreciated.

Sixto
91 300SE
81 300SD
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  #8  
Old 01-12-2002, 09:52 PM
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Sixto:

Looked at the photos of your brushes - they looked pretty wittled down to me. As I mentioned above, one of mine was 1/16" long; the other about 3/16".
New ones were 1/2" long. The brushes in the middle photo are way shorter than new ones. You'll have your ride back together in no time.
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  #9  
Old 01-16-2002, 02:10 AM
sixto's Avatar
smoke gets in your eyes
 
Join Date: Jun 2000
Location: SF Bay Area
Posts: 19,759
The $15 regulator from FastLane seems to have done it. I've never been so happy to see all the warning lights illuminated.

Thanks to everyone for helping.

Regards,
Sixto
91 300SE
81 300SD
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  #10  
Old 02-06-2002, 03:31 PM
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Join Date: Oct 2001
Posts: 507
stupid question

Hey, this may sound stupid to you guys, but i've never had to work with an alternator or regulator before. Where are they, and how do i get to them =P
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  #11  
Old 02-06-2002, 03:51 PM
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smoke gets in your eyes
 
Join Date: Jun 2000
Location: SF Bay Area
Posts: 19,759
The location of the alternator will vary from car to car but it's driven off the accessory belt so it'll be towards the front of the engine. The regulator on modern MBs is part of the alternator. Two screws hold the regulator to the alternator.

As mentioned above, the MB voltage Regulator album in http://photos.yahoo.com/tabijan might give you an idea. The pictures are of my 91 300SE.

Sixto
91 300SE
81 300SD

Last edited by sixto; 02-06-2002 at 03:57 PM.
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  #12  
Old 02-07-2002, 01:15 AM
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Location: LEMONT-CHICAGO
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Gotta love those $ 15 voltage regulators from Fastlane.
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