Sorry about that. I knew somehow that might lead to head scratching, but thought it would be the quickest way to differentiate the internal construction of the electronic speedometer gauge from every other Volvo gauge so you'd know (after a quick trip to Wikipedia) how easily a single hair of iron can mess it up. This type of meter movement ruled electronics before meters got light-up digits.

Back to the practicals. Since this wasn't your car before it happened, there's only speculation possible about who may have tinkered in there, hopefully not ruining things to deceive you on an odometer reading. I doubt it could be the differential sender causing the problem where you have a reading before even moving. The ABS shares that signal as an input (according to my '92 wiring diagram) so you might do some research on testing whether ABS is working and that no previous owner disabled its warning light.

Naturally, you could swap in a new cluster, but I believe 92 have a very narrow range of replacements. I'm sure both variants of the 91 model year are different (ABS was optional in 91 and employed a frequency multiplier module IIRC) and I've no clue about changes for 93. Maybe the behavior you see is a result of someone else swapping in the wrong cluster. I might be able to tell using the manufacture date stamped on the gauge itself; every one I've had apart shows this.

If you find the ABS is using the rear wheel sensor OK, then you might just disconnect the green/white wire leading to the gauge to see how that affects your symptom. The L-shaped connector that mates with the gauge's circuit board can be opened to release the pins individually. At the bottom of my web page http://cleanflametrap.com are a couple pictorials of earlier speedometers to help you envision this before tearing into your dash.

Then again, maybe it is all innocent, and simply replacing the electrolytic capacitor will make it right again.
--
Art Benstein near Baltimore

A bicycle can't stand alone because it is two-tired.