How does the RESUME function operate on the early cruise controls? I have a '79 truck with what appears to be the same transducer, I'd like to add the RESUME but I'm not clear how the extra relay actually works. It seems like the clutch/brake interrupt opens the resume relay, which drops the vacuum source but also changes the voltage/current on the HOLD terminal. I can't figure out how the controller "saves" the cruise setting while shutting the controller off.
I get how the old one button cruise stalk interrupts on brake, but the newer one is a mystery.


BTW I'm wanting to add a resume relay and an off/on/resume switch to my '79 to update the function, I think I can do this if I rewire it and add those two parts. The existing button should work for set and coast, then the extra switch would turn off B+ to the unit and resume. DPDT with one position being momentary for resume. I don't want to dismantle the column or add a late model stalk as it's 100% stock.

 

GM cruse controls of the '70s all had a RESUME function. The cruise control in your truck is most likely fubar.