It didn't. There is a problem somewhere.
You would use a u switch for turning off and on a light, like a light switch. It could be used as some sort of an electric converter to power anything in your house or where ever you are.
There are multiple ways to wire a switch. If power is fed into the switch box, a second light would be wired one way, if power is fed into the light box, the second light would be wired a different way. This seems like it would be a task better given to a qualified electrician or local handyman.
Check fuse and headlight switch itself. The switch and its plug are probably melted.
I would suspect the light is on to remind you it is in self cleaning mode. Since the light itself works, I would look at the switch.
In a setup with two switches controlling one light, you would use a wiring diagram that includes a power source, two switches, and the light fixture. The switches would be connected in a "three-way" configuration, allowing either switch to turn the light on or off. The wiring would involve connecting the power source to the common terminal of one switch, then connecting the travelers from that switch to the corresponding terminals on the second switch. Finally, the light fixture would be connected to the common terminal of the second switch.
You need a Battery, Light Bulb, Ammeter, Switch.
If a single pole switch is wired to be a master switch, the switch would have to be in the on position for any other control devices to operate. Turning the master switch off would eliminate power to all devices (and/or loads) which it was serving. For example, some homes have a switch to control their outside light. If the outside light has a photo eye (the light will only come on at night), the switch is the master switch. Another example would be the breakers in an electrical panel. Each breaker would be the "master switch" for the circuit it protects. The main breaker in the panel would be the "master switch" for the entire home.
I would turn power off and remove the switch plate,the switch itself may not be secure against the box sometimes there are no screws holding the switch to the box. next I would look at the switch itself if you do not have a meter to check the switch, replace the switch, switches are less than a dollar, also make sure the wires are tight on the terminals of the switch and the wires are not touching each other on the switch maybe some one was there before.
Stuck brake light switch, or a short to power somewhere in the brake light circuit.
i think light two would turn on because it is in the middle of switch a and b
If the fuses are good, then check the light switch itself. It could be that over time the current draw on the light circuit has damaged the plug-in connection at the switch. check the fuses
the brake light wiring often runs through the turn signal switch i would test power going in to the brake light switch on the pedal and power coming out when pedal is depressed if power is ok suspect turn signal or hazard switch