The heater attaches to the hoses for the cooling system. The heater itself sits very low in the engine bay, near the front left corner. I think you can find it by taking off the side grilles (where fog lights get installed) and following the power cord back into the engine compartment.
Are you absolutely sure it's not working? It's got no pump or lights, and makes no noise when plugged in. It takes 2-3 hours for it to warm up a cold engine (use a timer to get it to come on ~3 hours before your expected morning drive). On mine, the temp gauge will show 190 before I start the engine, but it drops way down as soon as the coolant is circulating. However, it doesn't drop all the way down, and is back to 190 much quicker than if the engine was really cold.