What is the most likely cause of my cruise control not working in my 85 automatic rx-7? Is it most likely the cruise control switch or something else I should check?

 

Have you "eyeballed" the mechanics? (vac hose, cable, etc)

 

When was the last time you looked at the computer (underneath the driver side bin)?

When you turn the cruise on, does the red light come on? If the light does come on, will the 'set' button hold the car at a steady speed?

 

Definitely check the vac hoses that operate the cruise. common for those to come loose...the little t-fittings will probably fall apart in your hands after 18 years.

Right on.

 

As said above check the vacuum hose at the T. It is probably cracked since it's above the exhaust. That's what happen to mine.