SAAB 900 and 9000 Cruise control diagnosis. This information applies directly to 1989 and later models, and only those 9000s without Traction Control. First of all, the most common problem will be a leak in the vacuum circuit from the pump to the servo. Remove the hose from the black connector of the pump and gently suck on the hose while watching to see if the throttle valve opens. Be sure that it stays open if you hold a vacuum on the circuit. If not fix the leaks. The hose itself is often bad. Replace it from the pump to the pedal switches if it has cracks in it. The next thing to check is the brake switch and the clutch switch if manual transmission. These switches are vacuum release valves as well as electrical switches. Check the integrity of both functions on both switches. Before you get too far along, Circa 1990 a cruise control lamp was installed in the dash. This should turn on when the cruise switch is turned on. It will work even if the control unit is bad, in my experience. If it does not work, be aware that an automatic transmission car must be in D, and that a bad neutral safety switch can cause this problem. On Manual trans cars that circuit is bypassed under the dash in the left kick well. Look for a brown wire and an orange wire. Sticks are brown to brown and autos brown to orange. You can bypass the Neutral Safety Switch on automatics, just don't try to turn on the cruise in reverse! Another problem that appears from time to time is bad connections at the pump, corrosion etc. There is a release valve in addition to the pump inside the pump body. Hence 3 wires. Sometimes the valve is not energized due to poor connections and that prevents the pump from opening the throttle. If I remember correctly, Power enters on the red wire from pin 1 (1992 and later) and grounding the other 2 gets you the respective action. You could also have a bad speed sensor, or the wire could have been knocked off of it. (plugs in to the back of the speedometer head, accessed through the speaker area on 900s. 9000s.... have fun. The speed sensor can be tested by checking to see if the up shift lamp works. If you have an automatic you can install a bulb in that location and see if it comes on or not. Quick pin testing is as follows: (SAAB NUMBER 4108643 AND 4108650 ONLY CHANCES OF A BAD COMPUTER ON other UNITS IS REMOTE) First ground your test light, and check to make sure it works. Pin 9 (red) & 10 (brown) should have +12V. Pin 3 (green) should light the test lamp when pushing the set switch. Pin 4 (yellow) should light the test lamp when pushing the resume switch. Now turn off the key and hook your test lamp to (+). KEY OFF!. Pin 8 (black) and Pin 5 (red white) should both be grounded causing the test lamp to light. Pin 5 (red white) should turn off the lamp when you push the brake pedal. If all these items check out you probably have a bad control unit.