Door Lock Circuits
The door lock circuit in the diagram above uses ground side switching (negative pulse control) containing two SPDT single pole dual throw relays. The system uses voltage reversal to control the direction of the door lock actuators. Apply voltage to one wire of the motor and ground to the other and the motor moves in one direction. Reverse the polarity and the motor moves in the opposite direction. This is accomplished with a lock relay for one direction and an unlock relay for the other.
A positive pulse door lock circuit is very similar. Power instead of ground is used to energize the relay’s coil. Some door lock systems omit the relays and use a thicker gauge wiring instead. These are often found on domestic vehicles. Late model vehicles sometimes contain control modules offering more features for door lock and security system control.