Hello, and Thank You for using Just Answer,
I'm going to give you the most common faults that I remember causing problems on these vehicles. There is a 14 pin cruise relay ( I believe to to located on the left side underdash area) , but not known to fail often. The brake pedal switches (yes there are 2) are the most common sources of failure, and if it's a manual transmission, the clutch switch as well. One of the brake pedal switches is for the brake lights, but the other, like the clutch switch, should be normally closed, providing a 12 volt signal to the cruise module (pin 3). These are notorious for failing, breaking, etc. They also provide a vacuum release that could cause a fault, even if the electrical portion of the system is OK. The switch is identifiable since it has a vacuum line attached to it. I've also seen the signal stalk cause faults, either from the cruise switch itself, or more commonly due to exposed and chaffed wires near the stalk pivot. You may be able to see the damaged wires without removing anything. Proper fault tracing the vacuum portion of the system requires a handheld vacuum pump and gauge.
Keep me posted, I'll try to talk you through diagnosis if needed, Bill