164 gauges fluctuations

[Jeff Matson <jsm8@domain.elided>]

Anyone know offhand where the grounds are for the instrument
cluster on a '91 164?  I'm starting to think I've got
something loose there.  Here's my symptom: sometimes when I
drive the car the voltage meter will read low (12.5 or 13
instead of the usual 14).  When this happens, the oil
pressure gauge will read 20% higher than usual, and the tach
seems high as well (well above 3000 at 70mph, which it
usually isn't).  The other three gauges (water temp, gas,
speedo) read fine at all times.  I originally thought there
might be an actual voltage problem, but nothing else is
strange, car always starts fine, etc.  Might I just have a
lousy connection behind the instruments?  Different grounds
for the two halves of the panel maybe, or something like
that?  This problem comes and goes, so I haven't pulled the
cluster to look yet, as I'd have to drive with it that way
for a few days to get something bad to happen.  Anyone else
ever see this?

Jeff Matson
Harvard, MA
'91 164 L
'74 2000 GT Veloce

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