Car Security and Convenience / Power Door Lock Types

Three Steps to Determine Door Lock Type
To determine what type of door lock switch you are working with, follow these three steps:

1. Locate the harness plugged directly into the back of the door lock switch. If there are no external door lock switches, you will most likely have a vacuum type system or an *aftermarket door lock system with relays, or have an added actuator that needs relays.

2. Next, with your multi meter, probe each of the wires in this harness and write down the readings during lock, unlock, and at rest positions of the switch. Be sure to measure for continuity to ground as well as positive DC voltage and pay close attention to any changes in voltage, resistance, and the duration of pulses. If the switch is illuminated when the lights are turned on, find this wire(s) first and ignore it.

 Door Lock Types Single Wire Systems There may be one, two, or three wires in the harness not counting the illumination wire(s), if any, and only changes in voltage and /or resistance on one wire to lock and unlock. Some of these will open a circuit to lock and ground a wire to unlock. Others will show a difference in resistance to ground or positive 12V DC during lock or unlock or both. Vacuum type locks will change polarity on a single wire to lock and unlock. ( diagrams )
 3 Wire Negative There are three wires in the harness not counting the illumination wire(s), if any. One wire has continuity to ground at all times. Another wire only shows continuity to ground during lock and (+) 12V DC at rest. The last wire only shows continuity to ground during unlock and (+) 12V DC at rest. ( diagram )
 3 Wire Positive There are three wires in the harness not counting the illumination wire(s), if any. One wire has constant (+) 12V DC at all times. Another wire only shows (+) 12V DC during lock and ground at rest. The last wire only shows (+) 12V DC during unlock and ground at rest. ( diagram )
 4 Wire Reversal There are four wires in the harness not counting the illumination wire(s), if any. One wire has constant (+) 12V DC at all times. Another wire has continuity to ground at all times. A third wire reads nothing at rest, and (+) 12V DC during lock and continuity to ground during unlock. The fourth wire reads nothing at rest, and ground during lock and (+) 12V DC during unlock. ( diagram )
 5 Wire Alternating (+) 12V DC There are four, five, or six wires in the harness not counting the illumination wire(s), if any. One or two of the wires has constant (+) 12V DC at all times. One or two of the wires has continuity to ground at all times. Another wire reads continuity to ground at rest, and (+) 12V DC during lock. The last wire reads continuity to ground at rest, and (+) 12V DC during unlock. ( diagram )
 Vacuum Type There is no external switch (switch is contained in the drivers door lock actuator) or it has three wires not counting the illumination wire(s), if any. One wire always shows continuity to ground. Another always shows constant (+) 12V DC. The third wire changes, reading continuity to ground or (+) 12V DC depending on the position of the door locks. ( diagram )
 Added Actuator(s) The two wires of the actuator(s) will normally rest at ground, if wired as shown in this diagram, but may rest at (+) 12V DC. Polarity changes on one wire during lock and on the other wire during unlock. *If you are dealing with an aftermarket door lock system, locate and measure each coil wire of the lock and unlock relays. Then connect to the wires that activate each relay accordingly. If the system has a relay module, it may also have two wires (pig tail) that will energize the coils of the internal relays. These will usually be negative inputs. Some will have both positive and negative inputs to work with any alarm or keyless entry without the need for additional relays. ( diagram )
 Special These applications will be similar to others, but will require additional connections, parts, or both. ( diagrams )

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