Need help on '90 200 instrument cluster lights

[Keith Lawyer]

My '90 200 has not been charging, and the alt warning
light is not coming on with the key.  What concerns is
me is that the light is inconsistent.  Sometimes it
will come on, sometimes it will not.

The exciter wire looks good so I pulled the instrument
cluster this morning (after a bit of cursing).

Lots of questions:

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?

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?*

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

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??

Bonus points if you're able to answer this quickly,
I'm trying to get the car back up ASAP, ie by this
afternoon.

Many thanks
Keith L

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