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Over time the electrical plugins at the headlight bulbs get real corroded but by spraying WD-40 into them and plugging them and unplugging them about 8 to 10 times usually takes care of the problem.
Carefully check the headlight connectors paying special attention to the contacts as seen from the back of the connector--they should all be inside the connector body at the same level. Sometimes the contacts inside the connectors become loose and you get intermittent operation of the exact sort you mention. Usually (but not always) just pushing the contact back into the connector will re-lock it.
Could this possibly be the light switch mechanism? Or would that cause all the lights to go faulty?
Headlights don't have a fuse they have a built in circuit breaker in the switch. I don't know what year car you have but if it's an older model c3 the dimmer could be bad on the floor causing either the bright or dims to intermittently work and you could have a bad connection or a bad bulb on whichever one doesn't work individually. Post the year of your car and I'll give you some information
First thing I'd check is to make sure the dimmer switch isn't causing part of your problem. I remember you now. I helped you find your problem with the tail lights. You need to fill out your profile, or start mentioning the year of the car in your question. Did you ever check the small fuse for your instrument lights problem we discussed?
Last edited by 65GGvert; Oct 25, 2015 at 02:09 PM.