Interior lights cycle from bright to dim and back

Sounds like a converter problem.
Contact your local service center directly or online here:

Most likely:
If it is a regular rhythm, look at your converter. The converter changes 120vac to 12vdc. Your interior light are 12v. A failing converter will cycle like that. Probably in the diode array and not servicable. I recommend one of the multi-stage converters. More $$$ but worth it. An alternator (on the engine) can do the same thing if the engine was running.

If irregular, it is varying loads on the power feed. Not much you can do about it except change where you hook up.