1989 GT Cruise Control Problems

I have a 1989 Mustang GT that has developed cruise control problems. When you set the cruise, it acts like it isn't doing anything, but if you take your foot off the gas, and you gently tap on the accelerator, then it will bring it up to the set speed. Then, once you take your foot off the gas, it slowly creeps down and won't go back up on it's own unless you lightly tap the gas again. Has anyone else run into this problem? The accelerate button also does nothing anymore, but the coast one does. All lights, horn, etc work. I would like to try to fix it my self if at all possible. I just don't know where to start looking. Any help is greatly appreciated.