The cruise control went out on my 1988 Hawkins on a P30 chassis. I took it to a good mechanic who determined that one or more of the fine wires the CC uses were broken. The column stalk switch was replaced with a new one, which solved the problem.
It sounds like you are enough of a mechanic to disassemble this unit yourself, and perhaps you have ruled out this source of trouble. I just thought I would mention it. I also had a similar problem with the wires for the Tow/Haul switch on my 2000 Chevy Silverado 2500. That one I was able to fix myself with some solder and heat shrink tubing.
