Speedometer/odometer in 1992 Ram B250 not working
 

I recently bought a 1992 Ram B250 cargo van and the speedometer/odometer won't work. I went to the junk yard and replaced the instrument cluster however the problem still exists. There are only two electrical plugs on instrument panel, one is "L" shaped and the other is round. I don't see where a speedometer/odometer cable would be connected.
Are the speedometer/odometer "connectors" mechanical or electrical?
The headlights, turn signals and half the dash lights work so part of it works.
Any thoughts on where to attack this problem from?
Thanks!

The speedometer is electrical, there is no cable. The sensor is down on the tranny, near the tail section.

thanks!

on the driver's side and it's a speed sensor--$23 at autozone

thanks....
 

I see that on the drivers side towards the rear just above the tranny oil pan there is a screw in sensor. Think that might be it? Thanks again guys.