Need help on '90 200 instrument cluster lights

Huw Powell human747 at
Sun Dec 22 22:33:19 EST 2002

my feeble additions to Brett's comments...

> 1) the alt bulb does not *look* burnt and contacts
> look good.  How can I test the bulb itself?  If I
> guess wrong (pos/neg) I blow the bulb, no?

as he said, no.  You cna use a meter, a 12v/ground power supply, or find
somewhere else it fits and plug it in.

> 2) can anyone tell me what wire should power the bulb
> when I first turn the key?  I wanna make sure it's
> being TOLD to light.  From my wiring diagrams I'm
> thinking gray/yellow??  Or would it be one of the
> multiple blue wires back there?  Can anyone even point
> me to the right *connector?*

It's complicated, and I believe no one truly understands it, even Hans &
Franz.  But basically the circuit is through that blue exciter wire to
the alternator, via the oil pressure control unit.

> 3) is it ok if I turn on the key with the IC removed
> entirely??

I ran my 82 coupe without a cluster, no problem except for the no
speedo/no tach confusion.

I think as the years go by and the cars get more complicated (ie, code
reporting and electronic instruments versus analog) this would be less
and less advisable, ie I agree with Brett.

> 4)finally, this might mean something to someone: when
> the bulb was not lighting I also got a weird hum from
> the dash/firewall area when I turned the key.  I'm
> thinking this might be the ABS control unit based upon
> the wiring diagrams.  Does this mean anything to
> anyone??

Do you have a low voltage battery condition?  If so, maybe the oil
pressure unit is struggling to do its job and buzzing.  I'm not so
familiar with the 200 layout, but I suspect this unit is near the ABS
one, so they might be easily confused as noise sources.

Huw Powell

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