Ok, so I've removed that pannel under the steering column. I've now located the ignition switch but I'm having trouble taking it out. Any suggestions or tips on how to get it out? It's in a pretty tight spot. Can hardly get any tools in there.
I'm also guessing that you have to stick a screwdriver in that little slot to push a clip to get the plastic plug out. Still, it's really hard.

Anyway, just double checking. If I take the plastic plug out, switch on the key and the lights don't come on then we know the culprit?

Answer
 

NO.

Removing the connector breaks all circuits, just like removing the car battery would..
No diagnostic data possible.


.

Hmm
 

Start the car.
Does it go to at least 13.5 volts.
When you raise the RPM does voltage go up, drop or jump around.

How old is the battery ???


.

Removing the Electrical portion of the IGN Sw.
 

with the Steering Wheel Locking Mechanism in place Is a Booger Bear!

There are three screws that hold the Elec. Sw. to the Locking Mechanism.

GSXR has pictures of the innards of a BAD Ign. Sw. Electrical and it shows the
Plastic Detents inside wear and don't close the Contacts.

You'll note he speaks the truth about the difficulty of R+R -ing the Electrical
Switch Portion EVEN WITH THE DASH "TOP" COVER REMOVED!

Here:
http://www.peachparts.com/shopforum/diesel-discussion/122926-cure-stuck-ignition-lock-2.html


Some idea of the difficulty:
http://www.w124performance.com/service/w124CD2/Program/Chassis/46-8010.pdf

Replacing the Electrical Portion of the Ignition Switch is the "Atom Bomb Option". You'll look for ANY other cause to your symptoms FIRST!

The Benstenator,
Great Picture! Almost makes me believe I could get to the Three self tapping
screws that hold the Elec.Switch onto the Steering lock with an Offset
sideways ratcheting Screwdriver set.

Do NOT, DO NOT,Do NOT buy any Electrical Ignition Switch for your 124.128
EXCEPT the O.E. Mercedes Switch! [NOT "O.E. Type" or "O.E.M."] It HAS to
have the Mercedes part number embossed/extruded on the Plastic switch cover.Along with the Three Pointed Star.

Looks like improper grounding; likely behind the instrument cluster. Loosen and retighten it.

Could be, but when I had a bad ground problem the gauges went crazy along with all the warning lights coming on.

Ok, so. I borrowed a working multimeter and threw it on the battery. W/O engine running it got 12.1 volts. Then we turned the engine on and. . . it went down to just below 11 volts. Then worked its way up to about 11.5 volts. Then I turned the blower motor on and it went down a bit, 11.3 and went back up after I turned the blower motor off.

So is that a definitive "alternator" problem or am I still in the dark.

Thanks for the input so far.

Grounds ("Clean, Bright and Tight")
 

Engine,Alternator,Instrument Panel,Etc.,Etc.

BUT ,You're not getting enough DC Voltage with the engine running.

anything less than 13V won't even charge the Battery. (14.1V to 14.5V is Optimal)

How many miles on this Alternator's Voltage Regulator?

You can pull the V.R. with the Alt. still on the Engine [From Below]

You're looking for BADLY WORN Brushes on the V.R. !

If you want to PERMANENTLY "FIX" the Alternator:

http://www.peachparts.com/shopforum/car-audio-multimedia/53236-installed-143a-alternator-my-w124-86-95e-class-photos.html

(Ignore the Alternator removal Madness in the following sequence)

V12 Uber Alles, Alternator Bearing Replacement in a W140 Mercedes Benz, by Brett Allison

(This is Oichan's alternator TOTAL rebuild on an 120 Amp Bosch unit)

Oichan's Corrado Alternator Rebuild.

(BBBBBUT,I'm afraid that reply #2 on this post MAY also be Involved)

hmmm, well I ended up taking the alternator off and we ran it down to ex-Checker to get it tested for free. It basically failed. They said it wasn't getting any readings. Which I kinda thought strange, since I was getting some voltage, but I dunno.

Something else we discovered is that there's some sort of fuel/oil leak that has been leaking on top of the alternator. At a quick look I couldn't see any obvious leaks from above. I'll definitely look into it more.

Soooo, I need to fix that leak before getting a new alternator on so that the new one doesn't suffer the same fate.

Any other inputs?

Check the "Weep Holes" on the Water Pump
 

"Something else we discovered is that there's some sort of fuel/oil leak that has been leaking on top of the alternator. At a quick look I couldn't see any obvious leaks from above. I'll definitely look into it more."

1.There are Two weep holes 180 degrees opposed to each other (Top and Bottom) on the Water Pump

OR

2.Oil leak from Valve cover gasket (?)

_________________________________________________________________

Yeah, the DMM doesn't Lie.
11.3 Volts with a running engine means ALL the D.C. power is coming from the
Poor Battery and NONE from the Alternator.

Ok, so I put in a new alternator. Just a regular old stock one.
The good news:
The warning lights have turned off.
I believe I've found at least part of the oil leak. It was coming from the timing chain tensioner just above the alternator.

The bad news:
Actually started before I got the new alternator in.
The glow plug light does not come on when it needs too. But after a minute or two of driving it comes on and usually stays for another minute or two.
Start-ups have become a bit rougher.

So from one problem to another. . . Would this be the glow plug relay or could it be traced back to the starter switch as well?

Pre-Glow Indicator Light in the Instrument Cluster
 

Youse gots to gets Dats FSM online !

http://www.startekinfo.com/StarTek/doclist.jsp
CLICK on the Third one down (W124 service library CD)
Then CLICK on CD 1 or 2
Then CLICK on ACCEPT the TERMS
THEN CLICK on the "continue" button in the bottom right corner.
[Ignore all the Folderol about needing Add-Ons or Plug-Ins.]


The Pre-Glow Relay on the OM602.962 and certain OM603.XXX engines is
"Electronic" ,NO 80 Amp Fuse,It "Senses" a dangerous condition and disables
itself until the condition is "Fixed".

BUT,your Relay is trying to tell you that you've got one or more BAD glow plugs!
(Or maybe BAD wires from the Relay to the Glow Plugs.)
That's why the "Hinky" Startup! Not all five Pre-Chambers are HOT and BURNING.(see the First scenario in the second Pictogram below.)

[Also,it's not unheard of for the Pre-Glow Relay's Separate Dedicated Ground
Wire to be Bad or have POOR connectivity.]

You'll also note the FSM rather Rashly states "Replace Relay" (?)
When these Pre Glow Relays can be opened up cleaned and serviced.

ok, so that thumbnail that you sent says to check the draw on each glow plug. . .
What would be the proper way to do so? Do I have to leave the key on a certain position, engine running? I'm not so good with these multi meters. . .

Anyway, thanks for that site, I've been needing some resources.

Answer
 

You need a DC amp meter to check draw.

.

Ohm them out
 

That's what they've been doing.

(Unplug the Plug that has the 5 Glow Plug feed wires and see what values
you get.It's kinda a "Seat of the Pants" Test.If one or more of the 5 wires
were bad or compromised It COULD look like the Glow Plug was the problem.)

The FSM MAY be referring to using an D.C. "Amp Clamp"(Hall Effect) type meter.
which would actually show the "Draw" of each Plug/Wire during it's cycle IN
OPERATION.This would also show you if the Relay were "Sticking" ON after the
"Afterglow" period.(But a simple 12V D.C. test light will show you that.)

I'd put a 12V D.C. test light on the Glow Plugs (Individually) during the "Cycle"
and see if the Relay is "Hanging Up" after the Afterglow.
[If it's Not,Then you have one or more bad Glow Plugs!]
Wellllllllll, You could go crazy and disconnect the Glow Plug feed wires at
both ends and Ohm them out for Continuity/Resistance,then there's REALLY
nothing left BUT the "G" Plugs.

The Ne Plus Ultra test of the Plugs is to hook them up to a Battery with
jumper cables and see if they get Blazing Red Hot at the tips FAST.
Do be careful if you go there...A functional GP will be like 1300 degrees "F".
Use something like a set of Vise Grip pliers to hold the Plug!
I like welder's gloves TO hold the Pliers.(AND Safety Glasses)