Ford products of that era are common for alternator wiring / plug faults. Should have a starting and charging system test performed to see whats going on. Alternator internal diodes go bad also and could turn the light on intermittently
You need to have your alternator checked , just drive it up to a auto parts store and ask them to check your alternator, they usually do this for free.Also take a good look around your alternator to see if there 's any loose wire's going to it.