i seem to be having some problems with trouble shooting my cruise not working. checked over the vaccum lines very well. checked the adjustment and ohm'd out the switch on the break pedal. was curious if there was a way to check the unit itself or if anybody knows of any other common faults these have. I did check the fuse. and lets say i have to replace the unit... what other makes and models will interchange? thanks
The unit should be the same on all 88-90 GPs for sure, I'm not sure which later years will also work.
Did you check the vacuum line coming off the check valve in that area that goes to the vacuum reservoir(it's just in front of the tire/fender area under the front bumper). Also, the vacuum line for the cruise that runs right near the strut tower is often in very bad condition from the turbo.
EDIT: Here's all the cruise control troubleshooting info:
http://s44.photobucket.com/albums/f14/platjblser/TGP%20Cruise%20Control/
The pictures(took pics since that's quicker than scans, they're still plenty good enough to read though) are arranged in the order that they appear in the repair manual. The first eight pages are the troubleshooting portions and the last three contain more general cruise control information. Remember to click the images again once they load for the full-sized versions. ;)
my first TGP had issues with the CC not working, until I found that I hadn't really set the brake switch/cruise cut off switch under the dash properly. Try hooking your foot under the brake pedal when driving and see if that allows it to engage?? Just a thought. Good luck with the diagnosis.
tried that under the brake pedal thing. i did check the adjustment and ohm out the switch to make sure it was working properly