Lights Flicker

Strange problem with my '89 XJ Wagoneer Limited. Seems that sometimes (not all the time), at night I notice the dash lights (and head lights) "flickering"...going brighter and dimmer together. Really noticible at idle, but also present at highway speeds. I've replaced the alternator less than a year ago.

Any thoughts? Any ideas on how to narrow down the cause?

Thanks in advance!

bad battery cables, loose connection somewhere or your headlight switch is going out.