Probably the speed sensor on the transmission.
I just acquired this 1994 jeep wrangler and the speedometer does not work. I understand it does not have a cable, so if it is electric i am lost . Help
You can fix the speedometer in your 1994 Oldsmobile 98 by replacing the speedometer cable. If changing the speedometer cable does not fix your speedometer you will need to replace the entire speedometer.
usually it's the speedometer cable that goes bad, you can reach behind the dash and unplug it from the speedometer and with some pliers undo it from the transmission. If you can spin one end and the other does not spin it is bad.
Check: Cable to trany, gear in trany, speedo head in cluster
how to fix speedometer for Toyota mr2
I need to fix the odometer and speedometer in a 97 ford explorer
Send to a speedometer repair shop or replace speedometer head
If the speedometer is not working it probably needs a new speedometer cable. If the speedometer is actually broken either take it to as speedometer repair shop or replace it.
My 89Chevrolet astro van digital speedometer stop working. How do I fix it
Most likely speedometer cable
May have to take it to a certified speedometer repair shop