The doorbell operates as a simple switching circuit. The schematic layout is one of the easier wiring schemes to work with in your home. A doorbell is a closed circuit consisting of a power transformer, a chime generator and the actual doorbell switch. This single pole single throw momentary switch temporarily closes the circuit, providing power from the transformer to the chime unit while the doorbell is depressed. Wiring a doorbell in your home is easy to accomplish with a basic understanding of this circuit and the right tools.
Disable the doorbell circuit at the circuit breaker to cut power to the doorbell's transformer. The transformer may be an individual unit or built in to the chime unit, which is the case with most newer doorbell systems.
Unscrew and unwire the old doorbell switch if necessary.
Connect the existing wire to the terminals on the new doorbell and tighten down. Which wire goes to which terminal is not important, as it will produce the same result.
Position the new switch and screw into place. You may need to drill new mounting holes if the switch is a different size or shape than your old doorbell.
Disconnect the wires running to the old chime unit, and remove it from the wall. Remember which wire attached to which terminal by drawing a quick sketch or labelling the wires with tape.
Run the existing wires through the hole in the base of the new chime unit and attach them to the correct terminals. Screw the unit securely in place and attach the cover.
Return power to the doorbell circuit and test that the new unit functions properly.
Always make sure power is turned off when working with an electrical circuit. Altering a circuit that is powered will result in electric shock.