It's the one on the passenger side - but that's for the ECM (I think). The one on the driver's side is the knock sensor.
The one you bought is the 2-wire sender for the gauge, mounted on the front of the engine.
AutoZone has repair info online on the menubar. It's info from the Chilton's or Haynes, one of 'em, and will help if you have nothing else. I have a '93, but the engines are the same, so here's a link:
http://www.autozone.com/autozone/rep...00c1528003d503
Have you checked your thermostat? It's quite possible it's stuck open and the truck never heats up.