Ah, the all-mighty odometer problem.. This seems to be an ideocyncracy in the later 240's.. They go out between 160-180K-miles.. I had mine fixed by a Volvo guy in Gainesville,GA(The European Specialists,, I think).. He was the only one in the region risky enough to pioneer the job. The problem is cuased by a small gear which eventually breaks.. I believe it was made of rubber and the rubber eventually dries up and breaks up too!

My trip-meter also failed the same month the odometer failed.. All together it only cost me $200 for both to be repaired.

I was going to get a used cluster from the bone-yard, but then I discovered that all the clusters in the 240's which matched the one in mine had the exact same problems! So that plan was scratched.

I'd get another cluster and see if you can get a working speedo out of the two you'll have. These instrument panels aren't expensive, used.
You've pulled out the little silver drive motor and verified that the tiny tan gear under it is intact? THis sounds like a classic case of gear failure. It can be a little tricky getting that speedo out and apart...
On my 91, I believe the one extra wire was for the SRS lamp. I thought another lead went to a double terminal in the center of the cluster behind the speedo- and it looked like a ground lug on the cluster, but it may not be. I thought it was a yellow or maybe blue and yellow striped wire. It's been a little while.
As Chuck noted, there's a white/red striped wire there, for the tach. Don't plug it into anything except the tach if you have one. The end is insulated so that it can be left disconnected.
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Rob Bareiss, New London CT ::: '87 244DL/M47- 225K, 88 744GLE- 209K, 91 244 183K. Also responsible for the care and feeding of: 88 745GLE, 229K, 88 244GL, 146K, 87 244DL, 235K, 88 245DL, 236K

is the striped 1 white/red stripe? that's for the large tach if you have it in the cluster. never plug it in the cluster if the tach is not there. good luck, chuck.