Headlight problem on my Ford Ranger

If the high beams never cause a problem, that should rule out the head light switch. The most likely suspect is bad contacts in the dimmer switch but also check the connector for signs of overheated terminals and a melted connector body. There could also be an intermittent connection in the wire going to the low beams.

If the high AND low beams are both affected, then it could also be the head light switch as well as the dimmer switch. If you can find used switches in a salvage yard you can try replacing one at a time to see if that solves the problem, otherwise you can do some testing with a test light or voltmeter. You would need a wiring diagram to know which wires to test on. You'd place the test probe on the wire leaving the head light switch, then watch if it goes out when the head lights go out. That will tell you if the problem is before or after that point in the circuit.

I might be able to help with the wire colors. I have a book for a '97 Ranger. That might be close enough.