I have copied this from your other post which may provide the clue to the problem:

"The previous owner said that the issue started happening, Right after he had the Instrument cluster Odometer repaired at a local radio repair shop. He never took it back to have it addressed, but that supposedly is when it started happening. not sure how that circuitry is possibly connected to the warning lights."

I am not familiar with the construction of a W126 cluster. If it is similar to W123, then the grounds between sections of the cluster are made via screws. Check that all the screws are there and that they are tightened down. Your alternator is fine so don't mess with it.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

I agree with you that the Cluster seemed suspect based on what the previous owner said, but this thread made me lean toward an alternator. On the other hand, the previous owner also was incorrect about his knowledge of what was actually repaired. He told me that the clock was repaired, but after i pulled the cluster, i saw a sticker from the repair shop, and it said that the Odometer was repaired, 3 gears were replaced and 2 capacitors were swapped. I called the shop to confirm that they did not repair the clock.

I will take the cluster apart and see if i find anything suspect. I will check the round connector to make sure the soldering looks good, and maybe re-flow each wire to pin connection.

__________________

Grey '91 350SDL 214k Dad's car
Beige '81 240D 4 Speed 254k SOLD
Blue '82 300D 225k SOLD
White '95 E300D 46k SOLD
Blue '87 190D 2.5 Turbo 315k SOLD
Brown '80 240D 4 Speed 716k SOLD
Beige '80 300D N/A 119k SOLD
Blue '85 300D Model 186k T-Boned

IIRC the PO of this thread had 3 bad rebuilt alternators in a row. He was extremely unlucky and what happened to him is highly unusual... 5 million to one IMO.

All you need to prove to yourself your alternator ok or not is a voltmeter. Hook it up to the battery and rev the engine as your bank of lights on the cluster changes brightness. If the voltage varies between 13 to 14 volts the alternator is fine. If it varies between 6 to 13 volts, you have a problem with the alternator.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Already did that test and the voltage was at 13.2 and increased to 13.7.

__________________

Grey '91 350SDL 214k Dad's car
Beige '81 240D 4 Speed 254k SOLD
Blue '82 300D 225k SOLD
White '95 E300D 46k SOLD
Blue '87 190D 2.5 Turbo 315k SOLD
Brown '80 240D 4 Speed 716k SOLD
Beige '80 300D N/A 119k SOLD
Blue '85 300D Model 186k T-Boned

That's normal and would not cause just those few lights in the cluster to bary in brightness. Why did you think the alternator is bad?

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

I also noticed a slight amount of static on the AM radio station when driving. thought that they could be connected to the Alternator.

__________________

Grey '91 350SDL 214k Dad's car
Beige '81 240D 4 Speed 254k SOLD
Blue '82 300D 225k SOLD
White '95 E300D 46k SOLD
Blue '87 190D 2.5 Turbo 315k SOLD
Brown '80 240D 4 Speed 716k SOLD
Beige '80 300D N/A 119k SOLD
Blue '85 300D Model 186k T-Boned

Unfortunately, the odds are much better than that. The problem is that the old Bosch alternators have an Achilles heel. The wires that connect the slip rings to the field coil run across the top of the magnet poles. At the factory, this area is coated in oven-baked epoxy to prevent the wiring from flying apart at high revs. I've had serial rebuilt failures due to the idiot tech installing new slip rings and leaving the wiring loose. I eventually sourced a replacement rotor and rebuilt the alternator myself.

I think the problem in this case is that there's carbon built up on the slip rings. Eventually the alternator will stop charging altogether, but for the moment it's simply unable to put out high current. If this is the problem, the fix is to remove the voltage regulator and run abrasive over the slip ring surfaces. Once they are clean and shiny, I bet the problem is solved. The only other possibility is weak diodes. Either problem would explain both the odd lights and the radio static.

FWIW, local instrument cluster grounds have exactly nothing to do with the warning lights. These lights are grounded through either the alternator voltage regulator or their respective devices. As long as the multi pin connector is sound, I think you can take a cluster problem off the table.

I will remove the voltage regulator and take a picture of where the bushings make contact with the armature. Is that what you are saying needs to be checked to be shiny and clean? Also i will check the multipin connector.

__________________

Grey '91 350SDL 214k Dad's car
Beige '81 240D 4 Speed 254k SOLD
Blue '82 300D 225k SOLD
White '95 E300D 46k SOLD
Blue '87 190D 2.5 Turbo 315k SOLD
Brown '80 240D 4 Speed 716k SOLD
Beige '80 300D N/A 119k SOLD
Blue '85 300D Model 186k T-Boned

The Slip rings should be shiny copper. Here, they are slightly discolored. Dress them with an abrasive, then finish them off with a contact cleaner spray. There's no need to disassemble the alternator, the rings are accessible once the regulator is removed.

This photo also shows the wire I was talking about...you can see how it's been torn away by centripetal force. Note the remains of the epoxy that held the original wire.

OK professor, please explain how a bad alternator can cause just the lights in the left bank of the cluster to vary in brightness with varying rpm and not the right bank of lights.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Here's the question I haven't heard asked: Is the alternator/battery light slowly coming on with the rest of the bulbs? If it is, I'd suspect alternator plain and simple.

The cluster lights are all switched on their negative sides by the devices that trigger them. Who cares about the cluster ground, they're not tied to it. They're fed a 12V feed and switched on the ground side, but also have a diode paralleled to the charging circuit. If the alternator is not producing power (no generation), the voltage on the field pin is low and the lights glow because they can pass current. If the alternator is working, the voltage is high and no current flows and no lights come on. The ONLY way all of those bulbs can light up in unison is to pass current to the alternator. The more current they pass, the brighter they light up. The other clue is the low charging voltage - 13.2V seems awfully low unless there is a lot of electrical stuff running. I'd suspect the slip rings on the rotor are worn out or contaminated.

__________________
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!)

Ok, I will be removing the alternator to inspect it, i think i remember seeing a little dark stuff on the slip rings, but dont think it was as bad as it was in the picture.

Instead of just doing a voltage test, i am thinking of checking what the current output of the alternator is. i will connect a Light to the battery and drain it for an hour or two. make sure the voltage does not drop below 11v. this should cause the alternator to send ample current to the battery to charge it. I will connect a current clamp to the alternator wire and see what the output is.

I have not had any issues with it draining and battery being low. i have driven it for 200+ miles, since i bought it, and battery has not been low. So i would suspect that the above test would show me that the alternator is able to charge, but not sure if the slip rings will cause the the light issue.

__________________

Grey '91 350SDL 214k Dad's car
Beige '81 240D 4 Speed 254k SOLD
Blue '82 300D 225k SOLD
White '95 E300D 46k SOLD
Blue '87 190D 2.5 Turbo 315k SOLD
Brown '80 240D 4 Speed 716k SOLD
Beige '80 300D N/A 119k SOLD
Blue '85 300D Model 186k T-Boned

Diesel300 did a good job of answering that...there's a potential across the indicator bulbs on the left side of the dash when alternator voltage is less than battery voltage. So the alternator would be high on the list of suspected problems. Since he's already replaced the regulator, he has to go deeper.

"The previous owner said that the issue started happening, Right after he had the Instrument cluster Odometer repaired at a local radio repair shop. He never took it back to have it addressed, but that supposedly is when it started happening."

So you think the above quoted text is just a coincidence and should not be investigated?

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Absolutely. Things just happen, the timing can be completely coincidental. Study the wiring diagram for a 126 cluster, there is ONLY 1 way those lights can all light together and that is to have a source to ground through the alternator field lead.

__________________
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!)