The two flow charts are very helpful to make sure the servo is working and that you have vacuum in the system. Just make sure you disconnect the cable to the carb.

My cruise control had two problems.

The (white) vacuum release switch on the clutch pedal was only giving the control module 6 volts and not the required 12volts. These switches are the same for auto or manual transmission. You can still buy these at oreillys, autozone or find them in the salvage yards

The (black) vacuum release (dump) valve goes on the brake pedal for manual transmissions. Mine had a bad o-ring and would not hold the vacuum for the servo. Not sure if you can buy these anymore, but I found a bunch in some of the early 80's caddys in the salvage yard.

The cruise control works great now...

wiring diagram.

Another problem I had was a bad ground at control module connector "J".

I know this thread is a little older but I just wanted to say thanks a million for posting this. I just decided to get my cruise control working and I hooked everything back up and nothing worked. Using your charts I found one of my SPS wires is broken somewhere. Still haven't fixed it yet but now I know exactly what all the wires do in the system.

Mine is/was working fine, but my cable from the servo up to my throttle bracket broke and I can't find a replacement. I need one with a ball chain on the end that connects to the servo. On the topic of this post, thanks for posting the wire diagram/flow chart. Will definitely help if I run into issues later on.