The "sensor" is for the ECU and could affect how the engine runs. Its also the one that the scanners will get their data from via the ECU.
It has two wires going to it.
http://www.ncttora.com/fsm/2000/Wiring%20Diagrams/Engine%20Control.pdf
Located near the top/front of the engine.
http://www.ncttora.com/fsm/2000/Repair%2...20Sens/comp.pdf

The "sender" is for the dash gauge. Its got one wire.
http://www.ncttora.com/fsm/2000/Wiring%20Diagrams/Combination%20Meter%20with%20Tach.pdf
Located near the top/rear of the engine (v6)
http://www.ncttora.com/fsm/2000/Repair%20Manual/Body%20Electrical/Combination%20Meter/loca.pdf
Troubleshooting info starts on page BE-41:
http://www.ncttora.com/fsm/2000/Repair%20Manual/Body%20Electrical/Combination%20Meter/insp.pdf

'97 4Runner, '06 F350, '86 4Runner, '05 WR450
http://home.4x4wire.com/erik