Where does odometer tie into tranny - 1991 Oldsmobile Ninety Eight Regency

CLuster speedo and odometer
both dead?
cable. or drive gears in tranny tripped.
easy to check. ?
sure.
at tranny cable free, spin it same direction as speedo needle.
speedo dont work (both odometer and speed) then the cable is bad.
if not work, tranny drive gears to cable stripped out. some are plastic

Vehicle speed sensor. This runs the odometer/speedometer. Top of tranny, a cable runs all the way to the back of the odometer.

they are spring loaded and mechanical. if a spring wears out or breaks it won't work. you can replace it with another one but the actual miles won't be there or you could go with a digital set.

check engine(service) light is tied to odometer. there is a sequence to reset yourself using a combination of key clicks and odometer buttons. Sunroof needs a fuse or the switch is most likely bad.

need a new speedo cable from tranny to back of dash

This might help a ton and save you money! So easy to fix, this video sounds like the same problem described! ABS light on, o/d flashing, check engine light on, tranny seems to be having issues, speedometer stops working. All fixed as described by the first answer james_hust , not tying to take your mojo but the video shows you what you need to do.

If the speedometer is working but not the odometer it's in the speedometer it's self. replacing the speedometer cluster is the easiest their available on ebay or your local salvage yard.
what happens is the trip odometer wears and sticks, theres a small motor on a circuit board with a plastic sun gear, inside the speedometer housing. it drives both the odometer and the trip odo
the teeth strip off the sun gear and odometer stops.

If it has antilock brakes, the sensor is on the top of the rear differential. This sensor usually drives the speedometer. check the sensor for an open in its windings and also the wire that connects to it for any breaks.

Sounds like either your speedometer cable, your nylon gear on the side of the tranny where the cable ties in, or the odometer itself is shot. One of those three will set you straight. If you are able, remove the cluster, take the cable off the back, and pull it out of the sheath. You will see if its broken or not from there. If not, slide it back into the sheath, then you have to find out where the sheath meets the tranny, and pull it off of there. Then, you can get someone else to watch the speedo as you turn the cable from the bottom. If it works, great, if not, then its your cluster/odometer/speedo. If it does work, the small gear in the transmission is shot.

the sensor is located on the back side of the tranny,have to get to it from under the car between the fire wall and tranny