Central Locking Help: Why are there 3 wires for each door lock?

Question

Tl;Dr: I want my hazards to flash with the central locking. I need to wire them up together with a diode to each side (left and right). The central locking has 3 wires

My questions are:

1. Does anyone have any better solutions for making the hazard lights flash with remote locking?

2. Does anyone have any idea what each wire does? Why are there three?

3. How can I test which wire is positive and negative? I have a DT-830B multimeter, with basic probes (sharp pointy ones). I don't want to splice into every wire and just use trial and error, and then tape up the ones which are wrong (I would only as a last resort).

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Long question:

My car has remote locking. However, the hazard lights do not flash with this. It is by design, and there is physically no connection between the flashers/hazards and the central locking control unit.

**Why am I asking? **

I often walk away from my car and lock it remotely. When it rains I don't want to have to fumble around to make sure the car is locked, and I always have the panic half a mile down the road of thinking "Have I locked the car?". The hazard lights would be incredibly useful, so when I lock or unlock the car, the hazards flash once. This is all I need to acknowledge that I have locked the car.

How:

I am planning to make them flash, by splicing into the wires in the Lower Left (passenger) A-Pillar. I have access to a dealership tool (TIS2000), with wiring diagrams for the entire car. I had a look at the wiring diagram for the central locking and the flashers/hazards.

My plan:

To spice into the central locking wire, and run two wires each through a diode (so when I indicate both of the indicators flash!), and then into the hazard light wire for each side.

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The good news:

The wires are literally right next to each other, and it's not a particularly difficult job to wire.

The bad news:

• The central locking has 3 wires! I have no idea which wire does what, and I don't particularly like the idea of splicing into each and having a quick test to see if it is positive or negative.

• The hazards will flash if I push the button to lock the entire car on the inside of the car, (Only on the driver's side). However, I never lock the doors when I drive, so this is rarely an issue.

Here are the wiring diagrams and connector locations

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Connectors in the A-Pillar

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Entire Central Locking Control Unit (Not very clear)

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Lock Motor Wiring:

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Hazard Lights/Flasher/Indicator Lights Wiring

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Full Size Images:

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https://i.sstatic.net/Gkod5.png

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My questions are:

1. Does anyone have any better solutions for making the hazard lights flash with remote locking?

2. Does anyone have any idea what each wire does?

3. How can I test which wire is positive and negative? I have a DT-830B multimeter, with basic probes (sharp pointy ones). I don't want to splice into every wire and just use trial and error, and then tape up the ones which are wrong (I would only as a last resort).

Answer 1

Looking at the diagrams, it looks like each lock has a motor and a microswitch to tell if it's locked or unlocked - presumably so you can't try and lock it when it's already locked or vice versa, or simply to reverse the polarity. The wire going directly to the motor (red and black) will be common to both. This wire will be positive for one action and negative for the other - though this seems a little odd to me, I'd have expected a solenoid with two separate coils. The other two wires will be separate for each action, one being positive and one negative.

You should be able to unclip the connector in the door and test the appropriate pins using the multimeter, rather than splicing...