Nearly all the cruise controlls use a cable activated by an electrc servo controll motor (old ones used to use vacume) Speed is controlled by electronic speedo signal (in the days of mechanical speedo magnets were fitted to drive shaft & pickup coil). So once the speed was set it would try & keep that speed. Much easier for an auto, in manuals there should be aswitch on the clutch pedal to disengage cruse control to stop engine from over reving. Also brake switch to disengage cruise. Fitted a lot of after market cruise controls to new petrol & diesel vehicles. Wth new vehicles Eg ford drive by wire throttle body, hasto be matched to engine computer as it now controls throttle opening, that bit takes a bit of geting used to. Daryl