Standard Cruise control looks for voltage ACROSS the brake light switch.. (See exception later).. On this type if the brake light fuse is blown, no 12 volts, if the brake lights are burned out, no 12 volts. and if the brake switch is closed (Pedal depressed normally) no 12 volts, and cruise says "Brakes on" and disengages.
IF the switch FAILS to close,, 1: Brake lights wont work, 2: Cruise won't disconnect (Turn it off to kill it).
NOW: the first cruise control I ever had had a separate switch that clamped onto the brake pedal arm.. It also had a dump valve.. Now that one worked great, Not only did it disengage but if the electronics failed for any reason it DUMPED the vacuum itself. They do not make 'em that way any more far as I know.
