There are only 5 parts to the cruise control.
--The vacumn diaphram that pulls the throttle.
--The control unit under the passenger seat.
--The On/Off Switch.
--The speed sensor (located inside the digital dash.
--and The set/resume/accel switch on the turn signal stick.
If you press the On/Off switch to on you should here a click under the passenger seat and the on light will turn on. If not then it is either the switch or the control unit.
(the car needs to be moving to test the next step)
If the "ON" light turns on then press the button on the end of the turn signal stick. If the "Cruise" light doesn't turn on then either the connections on the stick are dirty/corroded or the speed sensor is bad.
To test the speed sensor.
With the car sitting still pull on the emergency brake until the brake light turns on. Don't pull it all the way on though. Then start to move the car (you have to be moving over 5 mph) The car will now tell you that the "parking brake is on". If she doesn't say anything the speed sensor is bad and you need to get a new dash or live with it.
Also check that you don't have any vacumn leaks on the selinoids near the diaphragm.
I was lucky to find a digital dash in the junkyard that was in perfect condition and it fixed my cruise control and the voice warning unit.
I've had trouble with the connector next to the diaphram. Take the connector apart and put it back together a few times to break the corrosion, a spray with contact cleaner should also help, dry it off well, and give the contacts an extra push from the outside of the connector after you re-mate it.