Shifting gears which speed sensor shifts the gears on a 1997 dodge grand caravan? input or output?

The speed sensor is for Overdrive only, it does not shift the gears it sends the signal to the transmission control module that in turn signals the overdrive shift solenoid to engage/shift into OD.

Typically these vans carry a 41TE transmission. emissionwiz is correct in saying that the sensors don't shift the gears. They provide input data into a control module which in turn supplies or cuts power to various shift solenoids on the front of the transmission. These solenoid bodies are notorious for causing difficult problems. In the shop environment, the test is to install a known good set and check for performance. The solenoid block is typically covered in a black foam insulation, it is below where the cooler lines plug in just to the right of the bellhousing (if standing at the front of the vehicle).