I know from experience it will do that if it's drawing too much current. For example if you install a 100W bulb in place of the standard 55W it will cycle on and off about every 5 secs. So there's some kind of circuit breaker arrangement.hi everyone the left side off my headlight comes on when switched on then goes off and then comes on approx every 5secs then off i,ve changed bulb no good any idea sounds like relay problem thanks