1987 Mitsubishi Montero

My lights, headlamps and interior lights, are going from normal to slightly dim in a rapid sequence. They pulse from normal to slightly dim. Any ideas on what could be causing this?

This could be a sign of failing diodes in the alternator.
I would suggest having the alternator output checked a.s.a.p. before you wind up killing the battery and possibly getting stranded.

+1. Sounds like the classic case of a failing alternator.