What a coincidence.........I replaced mine today, after not having any speedometer activity.........and jeepers I now have a good steady speedometer and my cruise control works...........!! Remember now, that this 92 Cherokee is being resurrected for a knock around vehicle and had been setting in a wrecking yard for 4 months before I saved it!!!
If you crawl under the driver's side, up high on the end of the transmission you will see the sensor, unplug the 2 wire connector, using a 13mm wrench unbolt the one bolt holding the "wishbone" keeper and then pull it straight out. On the inside end of the sensor is a plastic gear on a long shaft which pulls out (mine slipped pretty easily). You will see a large nut which retains the sensor portion, you unscrew it and the sensor separates from the housing. This sensor you can get from a parts house, Autozone, OReilly, etc my replacement was made by Borg-Warner and cost app. $40 with tax.
Put them back together and slip it back in......MAKING sure you align it correctly for the number of gear teeth on your plastic gear. The number should be like 5 oclock for the wishbone to hit the lockdowns correctly. Then make your connection and give it a test drive.
You should be able to do this in 10 to 20 minutes easily!!
Good Luck!