[s-cars] Speedomter and tachometer are having a dance party without me

[Jason Butler]

I'm hoping there are some BTDT's out there for this.

My speedometer is for the most part accurate but sometimes, now getting more 
frequent,  will cutout and fall to zero.  When this happens my Tachometer 
will raise the RPM's about 20%.  Then when the speedometer comes back 
everything is normal again.

This sounds like a bad wire connection somewhere.
Things I've looked at:
    The IC, swaped to different one but still happens.
    Checked wiring to the speed sensor and all seems well there, I have 
continuity
    Looked at wiring behind instrument cluster and can't see anything 
obvious.

I've checked the wiring diagram but don't see any common grounds between the 
two.
Anybody have ideas?  This is getting annoying watching the speedometer 
bounce around out of the corner of my eye.

Jason
93 S4