chime for light out fix.
Had the same problem while on extended trip with fifth wheel in tow. Drove me crazy, but finally figured it out. It was a tail light bulb that had got hot due to the way the wires are on the end of the bulb making a bad contact. In turn they had melted into the bulb plastic base and would make contact intermidtently. Easy fix, just look at each bulb base carefully, takes more time to take each light apart than anything.