there should be three things plugged into your tranny. neutral position sensor, reverse sensor, and speedo sensor. the first two are on the front side of the tranny. The pic you posted with that sensor, it was either the neutral position or reverse sensor, don't remember which. The other one is on the backside more toward the starter/diff. if you can count three things plugging in, you have the sensor hooked up.
I know you have the sensor, I don't even know if it can be unplugged from the wiring harness. You had to have the sensor to have a working speedo before. You didn't swap the whole MSP wiring harness, did you?