Car Alarm Wiring - A lot of the Car Alarm Wiring that are already built into your car work as effective alarm signals. Most car alarm systems will honk the horn and flash the headlights when a sensor indicates an intruder, at the minimum. Cars can also be wired to shut off the ignition starter, cut off the gas supply to the engine or disable the car and car alarm by the Car Alarm Wiring. All you have to do is add an element to the pre-wired circuit to set up door sensors. With the new Car Alarm Wiring in place, opening the door, or closing the switch, sends an electrical current to the brain of the car alarm in addition to the inside lights. The brain sounds the alarm when this current flows. When the cylinder tilts one way, the mercury shifts so that it comes into contact with a second wire. This closes the circuit that is running through the mercury switch. When the cylinder tilts the other way, the mercury will roll away from the second wire which will open the circuit.