Where is the thermo control amplifier located on a 2001 Nissan Xterra?

Behind the glove box. The whole panel with the glove box comes out easily by removing a few screws along the bottom of the panel and pulling with firm pressure toward the rear of the vehicle. You will see the little plug (red, I think) on the evaporator case toward the bottom. Some early Xterras (00's, some 01's) have an old design and the improved design won't look much like the old one. The Nissan parts guy's 'service file' info will help with installing the new design. Good luck.