The cruise switches on the steering hub have resistors built into them. You cant really use the ones from the ghia wheel cos they wont fit into the dash anywhere. When u press the ON button, a 12V pulse is sent to the cruise ECU which turns on the cruise function. When u press SET, the 330ohm resistor is momentaraly switched between the cruise ECU and ground.... this tells the cruise to maintain that speed. When RES is pressed, a 1Kohm resistor is switched between the terminals and so tells the ECU to disable set speed. When OFF is pressed, the ECU function pin is grounded and the system shuts off. The diode is in place here so that the cruise ECU isnt effected by the horn relay.
The button schematic is attached