I have a 1993 240. Every few weeks, the ABS light comes on, and the speedometer and odometer stop functioning. Then after I turn the car off for a period of time, everything works ok for a week or two. Any suggestions where to start?

MAke certain your ignition switch isn't sticking. It may not be returning fully from the "START" position to the "ON" position. In "START" it does not power most of the accessory circuits, like lights and wipers and radio and of course the ABS system. A shot of WD-40 in the keyhole might fix it, or it may require replacing the electrical part of the switch. That's easier than it sounds, the lock is the really difficult part. The switch itself is easier.

Next time it happens, try to nudge the key back towards "OFF" just a hair- and see if the problem remains.
--
Rob Bareiss, New London CT ::: '86 244DL- 215K, 87 244DL- 230K, 88 744GLE- 198K, 91 244 180K

also, your model uses the speedometer signal for wheel speed on the rear. if you have a bad speedo sensor on the rear axle and you lose the signal that can cause this. check to see that the wires arent rubbing or something like that in the back.