Check all your turn signal bulbs , if a signal light bulb filliment breaks and touches the running light filliment , cross talk can happen . I've seen it before , watched two guys at work spend hours looking for a problem that was simply a bad bulb.
My interior light went out some time ago , it was a fuse in the power distribution box beside the battery, an easy fix that could have led to hours of searching had I not looked at fuses first.