Sporadic Headlight Problem

[wilkie]

Hello, on my '91 C2, at times the headlamps will not turn on when I turn the switch on. After repeated on-off attempts, they may turn on, and maybe not, in which case I drive on using the fog lights or high beams (using the flasher switch). Eventually, the headlights will come back on. Once on, they seem to stay on and won't go out. Any suggestions on trouble shooting? Is this a switch, fuse or relay issue?