If the truck has the carousel option the prox switch will be located at the left front wheel inbetween the other 2 sensors, probably going to be hard to see easily, you will have to rotate the wheel or remove the cover plate to see it(if it has a cover plate installed). On the dash there would be a switch clearly marked with a pict-o-gram showing the wheels in carousel mode.

There is no controller, everything goes through the relays.
If the relays are working properly they should illuminate when turned on, should be orange led indicators back near the connector end of the sensor. The ECM mounted on the engine is for the engine operations ONLY.

One of the most common problems i've found is the sensors get knocked out of adjustment causing issues like this one you have.