Headlights go on and off when engine is hot

Went to a cruse-in on a hot night. Stuck in traffic for about an hour. When I left it was dark. When I was about 5 mins from home the headlights kept going on and off. The dash switch may be the problem (dash lights don't dim properly, ordered a new 1) however could it be the headlight relay or another problem? All the other lights work, tail lights, parking and turn signals (they don't go on and off).