In my Bentley guide, they say that the CC is indeed connected to ground through the brake light circuit, or something like that. The only thing I haven't tracked down of the checkable items is the actual CC switch, a lever on the column. And BTW, it doesn't even begin to work. It behaves completely dead.
I took one of the servos apart one time, years ago, cuz I had about 3 of them
, non of them worked, so I thought, why not dissect one of the PsOS.
It looked like strictly an electrical device. No vacuum hookup anyway. If I find one of the others, I'll bust it up and post a pic. I found one web site back when who claimed to be able to refurbish the units for a modest price. I could never get them to accept my unit in the mail. I couldn't figure out what their trip was.
Best I can gather through the years (it's not a major priority but I've always had an ear out for it) the computer brain is what is usually bad, if none of the clutch, brake, or CC switches is bad that is.
I dunno, the advice of my metal fabricator guy neighbor at my warehouse is sounding more astute all the time. He just bought a new Dodge with dually, 1 ton I guess, w/ Cummins diesel. He sees me working on my rigs all the time and a few days back he said, "What you need to do is take off the radiator cap, hang it down from the top of your garage , and back a new car under that sum-*****." He's one of them California guys you hear about.