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Discussion Starter #1 (Edited)
My instrument lighting hasn't worked since I bought my car two weeks ago. I checked the bulbs, and they are all fine. All the other dash lights have always worked just fine, including every idiot light in the instrument panel.

I discovered reading here last night that my instrument panel has a separate dimmer from the rest of the dash. I tried it, and it had no effect. My Bentley manual isn't any help on this, but is there a separate in-line fuse in this circuit? Is this dimmer rheostat known for failing on its own? Is there a separate connector that may have loosened or corroded that I could find and troubleshoot?

Thanks for any help here,

Scott

P.S.--Anyone know where the instrument panel's ground connection is? I just haven't been able to see it through my speaker hole, but it has to be somewhere.
 

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The instrument cluster lights on my 900 dip if I push the dimmer thing a little to one side. Can't remember having read of them failing, but it seems a reasonable guess if you've already checked out everything else.
skucera said:
Anyone know where the instrument panel's ground connection is?
I think it's one/both of the two bolts on the lower left-hand side of the cluster:


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Scott--

The dimmer rheostats rarely fail, but their behind-dash mounting locknuts loosen with age so they spin around uselessly when you try adjusting the brightness.

With pliers, pull out the switch to the left of the dimmer; this will give you access behind the dash. Check that the dimmer isn't spinning as you turn its kn0b. If it is, either tighten the dimmer's locknut by hand, or just set the brightness to max. while holding the dimmer still and forget it:)
 

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Discussion Starter #4
Checked most everything

Actually, since I wrote my first question, I didn't get any replies. I ammended my post to ask if anyone could describe the location of the instrument panel ground stud. Last night I measured the voltage across the two sockets on the plug that connects to the back of the cluster... it was a very reproducible 4.78v. That confirmed for me that the ground was corroded, or the connection for the power side was. That sort of voltage is only enough to get a 12v bulb to glow dimly, but not enough to shine through the green filter gels

Looking through my speaker hole, I still couldn't find where those pesky green and black wires went to. They disappear between air ducts, headed straight down. This weekend (Fourth of July) I'll have time to hunt for the other end, but I really don't want to take the whole dash off if I can just reach that grounding stud under the dash somewhere.

Does anyone know where this little puppy is?

Scott



P.S.-- Professor, thanks for the advice, but it is the in-cluster dimmer that's affecting me. I have no idea why US cars have two dimmers. Maybe an engineer was building up courage to offer that "simple" lighting mode I read about on newer Saabs where all the dash lights are dimmed except the speedo, unless there's a need to show that data, like high temperature or low fuel? My dash dimmer works just fine. It's my instrument lights that are out.
 

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Maybe you could splice into the black wires (which go to this mysterious ground point), and connect them to another ground?

One possible location is the dash attachment screw at the base of the windshield, accessible through the LH speaker hole.
 

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Discussion Starter #6
Hmmm....

That's a really good idea. There is an extra set of pins on that IC trace for another set of green and black wires (don't ask me why). I could simply run an extra ground from that dash mounting bolt to this extra ground pin on the circuit. What an elegant solution!

Scott
 
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