I drove about ten miles this morning and noticed that all of the instruments, except the clock, stopped working. The car runs fine and everything else seems to work. I checked the fuses. All okay so I rotated each one. Still no instruments. I also noticed that the big relay was buzzing when I turned on the ignition like a relay was closing all the way. I pulled it out and put it back. Still nothing. I don't believe this relay controls the instruments but maybe I'm wrong. Any suggestions?
Thanks
Dave

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1986 300SDL

Replace the instrument fuse, it's cracked. Looks OK, but isn't conducting.

I'd replace all the fuses, the rest aren't in any better shape (bet they are all corroded, eh?).

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

No, actually, I went through all of the fuses a few months ago when I bought the car. In fact, according to the fuse diagram, not all of the instruments are connected through a single fuse.
Thanks
Dave

__________________
1986 300SDL

Hmm... OVP relay gone bad? Instrument panel ground wire off?

This is a new one for me. My TE had all the instruments fail, but that was a fuse.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Peter,
Just for fun, I did replace the fuse and no luck. That relay I mentioned in the first post is buzzing away. Guess I'll start with that.
Dave

__________________
1986 300SDL

The buzzing relay indicates a primary ground is broken; it is trying to back feed.
Now, your second clue is the sudden failure of the instruments.
The only thing all W126 instruments share is the central ground point.
Sad to say this ground point is roughly six inches behind the instrument cluster, and can only be reached by pulling the cluster out.
You will need the special tools and a large batch of patience, to get the cluster out without secondary damage.
I would wager that both issues are the same ground lug.

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1983 300D
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Thanks for the tip! I pulled the panel a few months ago to change the temp display. Maybe I dislodged it slightly at that time. I'll check it tomorrow.
Dave

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1986 300SDL

Not communicating clearly.
The central ground lugs are bolts with hords of Brown wire under them, this is against the engine compartment bulkhead.
Cleaning, testing and repairing in that area is a major PIA for the best of us, there is not enough space for hands, tools or eyes.
This ground lug area is known for corrosion...

Dave,

Yet another recommendation. The guages on my SDL would go to 0 when I stepped on the brake pedal. I removed all the relays ( around the fuse box), cleaned the pins, and re-inserted. This seems to have fixed the problem. Note, I pulled a silver relay that is a shade more to the center than the fusebox. It had a 10 amp blade type fuse on the top of it with a plastic cap. The fuse was loose in the metal knotches that held it.

This may not help but is quick and easy to try. Good luck.

Chuck

I have found that when my key switch returns a little too far counter-clockwise, all my instruments go dead. The car still runs though, it's just the instruments.

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Michael LaFleur

'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
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