The K40 is an archaic device. If I were you, I'd actually remove the entire unit and replace it with a Valentine 1. I digress.

To answer your question, the K40 radar system consists of two sensors (one front and one rear) USUALLY mounted somewhere BEHIND the front/rear bumpers (likely mounted on the bumper support bar itself). You can't miss the boxes - they are black and are slightly larger than a pack of cigarettes.

In short, you will likely have to remove your bumper to locate the rig(s).

Note: The position of the radar sensors is what really hurts the K40 system - not only do the sensors have to sense THROUGH the bumper, they are also mounted very low.

Good luck.