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Old 11-20-2022, 09:42 PM   #1
Brickhead1988
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Default Instrument cluster elec. wiring diagram 88 240

Lights in the cluster don't work. Bulbs are good. Fuses are good.

Turn signal, brights, ebrake all seem to be okay. Been driving with a headlamp around my neck at night...

Does anybody have an ewd handy? Or a source i might be able to download it at?
Bentleys ewd might as well be gibberish afaic.

Thanks guys!
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Old 11-21-2022, 09:26 AM   #2
cleanflametrap
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Although this is for a 91, I believe the theory applies. Check whether the lighting in the center console is also out, because it also depends on the dimmer rheostat, a common failure point.

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Old 11-21-2022, 04:00 PM   #3
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Just another version, from (apparently a 1988) 240 PDF.
Illumination circuit isolated + highlighted.
In from #16 on grey, through the rheostat to the bulbs, grounded with black.

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Old 11-21-2022, 10:48 PM   #4
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QUOTE=cleanflametrap;6300367]Although this is for a 91, I believe the theory applies. Check whether the lighting in the center console is also out, because it also depends on the dimmer rheostat, a common failure point.

[/QUOTE]

Thanks Art! And MasterBlaster! Much appreciated!

Do you have a source for any more ewd's? It smells like my cluster was domiciled by a skunk that somehow caught on fire.

So that's probably my problem. :(

After a few drinks I'm pretty good with a soldering iron.
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Old 11-22-2022, 12:08 AM   #5
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Have you checked the dimmer knob to the left of the cluster yet? i.e jumped the two wires together?
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Old 11-22-2022, 12:17 AM   #6
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Have you checked the dimmer knob to the left of the cluster yet? i.e jumped the two wires together?
No, Khrrck. I'm on the road at the moment. I haven't explored the rheostat. I'll try it in the the morning. Happy Thanksgiving!
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Old 11-22-2022, 08:55 PM   #7
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No, Khrrck. I'm on the road at the moment. I haven't explored the rheostat. I'll try it in the the morning. Happy Thanksgiving!
You as well!

if you have a voltmeter handy you can also check for 12V at the fuse, the rheostat and at the feed to the cluster.

If you do jump the two spade terminals together make sure to wrap them in tape or something so they don't short out against any of the headlight or foglight switch terminals back there.
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Old 11-23-2022, 12:22 AM   #8
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Originally Posted by Khrrck View Post
You as well!

if you have a voltmeter handy you can also check for 12V at the fuse, the rheostat and at the feed to the cluster.

If you do jump the two spade terminals together make sure to wrap them in tape or something so they don't short out against any of the headlight or foglight switch terminals back there.
Yessir got my clampon ammeter on me.

Much appreciated for the recommendations Khrrck!

But I have a bad feeling the inst. cluster is needing a colonoscopy.
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Old 11-23-2022, 12:33 AM   #9
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Yessir got my clampon ammeter on me.

Much appreciated for the recommendations Khrrck!

But I have a bad feeling the inst. cluster is needing a colonoscopy.
Happens to the best of us. Good luck, at least the LH 2.2 era clusters aren't too hard to find.
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Old 11-24-2022, 12:20 PM   #10
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Originally Posted by Khrrck View Post
Happens to the best of us. Good luck, at least the LH 2.2 era clusters aren't too hard to find.
I have the Tac. So they're just mightily expensive. Might as try to fix mine...

BTW in case i royally screw that up is the part for my particular cluster K9800?
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Old 11-24-2022, 10:04 PM   #11
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Thanks guys. Among a few things, was a bad rheostat.

Try to see if PnP has any.

Thanks again for all the help!
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Old 11-25-2022, 12:34 AM   #12
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I have the Tac. So they're just mightily expensive. Might as try to fix mine...

BTW in case i royally screw that up is the part for my particular cluster K9800?
K9800 is the number of wheel revolutions per mile for that speedometer. It is different between early/later cars (or ABS/non ABS some years) and between sedans/wagons.

However the PCB for the cluster is identical as far as I know between all the later 240 years. So you can swap your K9800 speedometer and your tachometer into any cluster (or perhaps transfer a good PCB to your own cluster, depending on the condition/finish of the plastics and such)

You can even replace the clear plastic or warning light label strips if you get daring.

Finally - if someone knows the wattage rating / resistance range of the rheostat, you might be able to order an appropriate panel mount generic one off Digikey or something. Not sure there's any good ones left. You can also try bathing yours with a nice spray of contact cleaner down the shaft and spinning it for a bit to see if that helps clean up any of the corroded surfaces.
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