Cruise Contr out - 90 Cam 6cyl Auto SW

Seems I saw somewhere online a flowchart for checking what’s wrong with my cruise control. I think it used a pocket tester with probes or something. Clue me in on where this is or how to check the problem. Thanks guys.

The first thing to check is if there’s a brake light out. If there is the cruise won’t work.

Tester