The baffling nature of Mustang headlight switches - what to do when they act up.
We've been over this one before, but it is important to your safety. Do you experience flickering instrument lights? Have you ever had your Mustang's headlights cycle off, then, back on, then, off? Both problems can be traced to faulty headlight switch operation.
Why do instrument lights flicker? The answer lay in your headlight switch's rheostat - also called a variable resistor or potentiometer. When you dim your Mustang's instrument lights, you are creating resistance to the flow of electricity. As you dim the lights, you increase resistance via the resistor coil at the front of the switch. Over time and use, this coil becomes corroded and dirty, creating a whole bunch of resistance to the flow of electricity. You can correct this problem with radio/television tuner cleaner found at the nearest Radio Shack. Tuner cleaner has a high evaporation rate. Spray the resistor coil and run the dimmer back and forth to clear debris. Instrument lights should work like a champ.
Headlights that cycle off and on do that because the circuit breaker built into the headlight switch has dirty or corroded contacts. Dirty and corroded contacts cause resistance and heat, which "fools" the circuit breaker to cycle lights off. Never mistake the cycling of lights as only a circuit breaker problem. When there's a low grade short circuit, the circuit breaker will cycle lights off and on. If there's a solid short to ground, lights will not come on in the first place.
Cycling headlights mandate thorough inspection of your Mustang's electrical system between the underdash and headlights. Dirty and corroded circuit breaker contacts call for headlight switch replacement.
Headlights that are dim - a brownish, yellowish dim suffer from a poor ground. Always check your grounds when electrical gremlins surface.