Curious, before I dig in, if anyone has a place to start for me to figure out a strange electrical issue in my 83 300SD.

When I turn the key to start the car to the "glow plug" mode (before you crank), my other dash warning lights don't come on. Rarely they might, but 99.9% of the time they do not. The glow plug dash light does come on and turn off correctly. It seems there is a drain going on right now on the battery too. The horn seems to be very intermittent and sometimes blower motor doesn't want to work.

This seems to have started just recently (I have been fixing up the car). I changed the glow plugs and glow plug relay last weekend and right after that is when it started. The glow plug relay was pulled from a junk SD, but was a year or two newer and the ID numbers didn't match (junk yard said to bring back if it didn't work so I wasn't too worried). But, the relay seems to work fine for starting the car so I thought it should be okay.

I was planning on putting the old glow plug relay back in, changing the very sloppy ignition switch, and check the fuse connections under the hood to make sure they were making good contact. But, after that....I am not sure what to look for or check.

I am wondering if there is a relay somewhere that might be worth checking or if there is a "fusible link" somewhere in these cars (had a 525 bmw with a bad fusible link before so I know how gremlinish they can be).

I have "in laws" in town now.......so this would be a GREAT time for me to stay busy working on the car! lol

Does anyone have a clue?

Since the overwhelming response, lol, I decided to keep checking things out to get more "clues".

The alternator dash warning light "dimly" lights up with the engine running. In fact, it dimly lights up even with the engine off too, but the key in the running position (before cranking).

I had the key turned to the "running" position, where the dash warning lights are supposed to be on (before you start the engine) and I went exploring to see if I could get them to come on. I had the "father in law" sitting in the car watching the dash lights (I think he can't stand his wife either). Messing with the fuses did nothing (in the fuse box). Moving wires and checking connections did nothing......BUT when tapping on the back of the alternator did change the problem.

Actaully, tapping on a very small metal box at the top and back of the alternator seemed to be the issue. I did not mess with it when the engine was running (it was dark), so I am not sure if the "battery" alternator charging light went out with the engine on.

This box is VERY small and is attached to the alternator with a screw on one end (the box is actaully more rectangle) and a wire coming off the other end that loops around down to the alternator. As I looked the best I could...it looks like there is a voltage regulator down further on the back of the alternator. I say that because looking at "electrical parts" online....importec.com has a "box" (like on old BMWs) type regulator and the typical brush type (so it says to check what you need).


So, anyone know what the heck I am seeing? Or is this all part of the typical voltage regulator issues and just replace it and it should work?

Rick

That is your voltage regulator.
Order a new one, they are cheap.

PART NUMBER SEARCH RESULTS WITH PRICES
Vehicle 1983 Mercedes Benz 300SD
Part: Voltage Regulator
F4010-39368 Voltage Regulator Bosch IN STOCK $33.26

F4010-108169 Voltage Regulator Germany IN STOCK $25.25

http://catalog.eautopartscatalog.com/mercedesshop/sophio/quote.jsp?clientid=catalog.mercedesshop&cookieid=1OI103FLR1OX03KERU&baseurl=http://catalog.peachparts.com/&partner=mercedesshop&year=1983&product=F4010-30110&application=000272329

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I totally agree with sir whunter on this one...I JUST had this happen last night on the 300SD and I rolled into town (200 mile trip) with only enough power to work brake lights and turn signals.
Dim glow, no lights when starting, sounds very similar. Eventually you will find that your battery will be dead (not fun).

You can either replace the brushes in your current regulator or just replace the regulator (with new brushes included).

The former is cheaper but requires you have a soldering iron. The latter is easy, a little more expensive, but only requires a two screw installation.

ALso why you have the reg out, check the slip rings (the things the bushes rub agaist) and feel for DEEP ruts...slight ones are okay but deep = bad

Thank you guys for the help. Ordered the part...will post later if it worked.

Rick

Well, I got the voltage regulator in the mail late yesterday with about an hour before dark.

All I had to do was crawl under the car with a stubby screw driver (didn't have to jack it up). Went to the back of the alternator, took out the two screws holding the voltage regulator in, slipped out the old one, slipped in the new one (wriggled it around to make it fit), and screwed the two screws back in.

The "brushes" on the old regulator were worn all the way down. When I got back into the car to start it, the dash lights didn't work the first time I turned the key, but I started up the car and the alternator light was on pretty full. Remembering from other posts I "revved" the car a couple of times. The battery light went off and when I turned off the car to check to see if the "dash warning" lights worked and they did. After driving around the car and stopping here and there, everything works great!

Yep most likely the new brushes just needed a little better seat on the slip rings when you popped the new reg. in.

Glad its workin well for ya, did you happen to check the condition of the slip rings themselves (the things the brushes ride agaist?)

WHen that wears out this cheap fix will no longer work hehe.