Not teribly difficult, it's at the front near the top of the engine itself but there are 2. Theone for the EFi has a rectangular plug like an injector plug and the wiring is in the same loom as the injector (on the 3.9 at least), whereas the sender for the guage has a single wire and is the traditional round type. both are close together and behind the dizzy IIRC, very close to the thermostat.
