I have the same problem. I set my cruise control, it lights up but, nothing happens. The only difference is that it sometimes out of the blue will work but, 9 times out of 10 it won't. Anyone have a fix for this??
Another simple/common thing to check is your clutch pedal if you have a manual tranny. If you recently changed your clutch and/or adjusted the pedal, it might not be fully depressing the upper clutch switch which would prevent the cruise control from engaging. Easy fix if that's the case: adjust the switch. This happened to me when I replaced my clutch...
Does the light come on, key on, engine off? It won't work with the light off. Assuming the fuse is okay check imputs to relay located at F/B 1. Next would be to check imputs to the ECM which is located center of dash. I've had trouble with the backside of the switch coming loose - to check this "squeeze" the switch with one hand and try to turn it on - monitor the light. Hope this helps.
Pull the engine codes. If you get a code 42, it could be very likely that you have cracked solder joints in the odometer, which will cause the cruise control to not work sometimes. I remember someone else once mentioned that it could be the actual wiring in the steering wheel column. I'd first start by trying to pull some codes though. If you have an OBD1 car, it's pretty easy to pull the codes. Check on www.mkiv.com.