3-Wire Door Locks
3-wire door locks can be either positive (diagram below), or negative. There is either a constant ground or positive wire that makes contact with either the lock or unlock wire when the switch is pushed. The idea here is to add relays that will make the alarm’s lock and unlock outputs to do the same thing the switch does. 3-wire door locks are used by a lot of Japanese cars. There is no need to cut the factory wires, just strip the insulation a bit and add the alarm wires (make sure you have a good connection – solder if possible).
5-Wire Door Locks
5-wire door locks are a bit more complicated. While the switch is off, both wires (lock and unlock) are grounded. When the switch is pushed for example to the unlock position, the unlock wire gets disconnected from the ground, and connected to +12v, activating the actuator. Same applies to the lock wire, but this time the voltage is reversed, moving the door lock actuators in the opposite direction. Here you have to cut the factory relays and hook up the aftermarket relays as shown. On the diagram, the “to switch” end of the wire is grounded and the “to solenoid” end of the wire either locks or unlocks the doors if given +12v.
Converting Manual to Power Locks
On some cars such as older Isuzu Rodeos a solenoid has to be added in order to make the other doors lock and unlock. The driver’s door lock does not have an actuator, it acts as a switch, so that when the lock goes up and down, it controls the power locks in the other doors.
Actuators can be added to virtually any car that has no power locks. One actuator is needed per lock. The circuit below will control all the actuators, locking and unlocking all doors at the same time. A grounded switch can also be added where the alarm hooks up to lock/unlock the doors manually. Note that the diagram is for alarms that have negative (ground) pulses for lock and unlock. If the alarm you are installing has positive outputs, then simply hook up the “85” terminals of the relays to ground (-).
Please keep in mind that the diagrams apply to most GM, Chrysler’s and Fords, but not ALL, so all wires should be checked before any connections are made. There are other ways in which factory locks are wired up that don’t fall in either the 3 or 5-wire categories, such as Ford Probes which use different voltage levels, Toyota Camrys with child safety locks which use diodes, and Mercedes, and other German cars that use vacuum door locks.