I have driven many grain trucks and seen them in several locations. The most common location is to the left and below the steering column. I have also used some trucks that had them in the radio holes, and right of the steering column. I driven two Chevy grain trucks that had them on the floor between the seat and the door on the drivers side. I personally liked that location as it was natural to just reach down with your left hand and actuate the knobs while still being able to look in the mirror. Maybe it was just easier for me since I was only 11 years old at the time. These same trucks also had the fuel tank switch in that same location. They were an AD truck and my dads 63 grain truck.
Ralph
