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On the legacy, there is a wire running between the driver's door and the control unit. Actually there was a bunch of wires, but I only needed to use one of them.
If you cut the wire the doors will lock. If you connect the door part of the wire to ground, the doors will unlock. When you disconnect it again, the doors will re-lock.
The cobra system I fitted had 3 wires to interface to the door lock system. Let's call them A, B, and C. To lock, it would connect A to B for 2 seconds. To unlock, it would connect A to C for 2 seconds.
If you look at the attached diagram, you will see how I used a relay to make it work.
i) If the doors are unlocked and I want to lock them:
The signal coming from the control unit is connected to ground. So the alarm connects A to B, which closes the relay and breaks the connection between the control unit and door. This causes the doors to lock. After 2 seconds, the alarm breaks the connection between A and B, which releases the relay, but that doesn't matter because the mechanism is now in the locked position, so the signal coming from the control unit is now floating (ie. not ground).
ii) If the doors are locked and I want to unlock them:
The signal coming from the control unit is floating (see above). So the alarm connects A to C, which grounds the wire causing the doors to unlock. After two seconds, it breaks the connection between A and C, but that doesn't matter because the mechanism is now in the unlocked position, so the signal coming from the control unit is now ground.
I hope that makes sense and that it works the same way on the SVX. If you can't find a wiring diagram, have a look behind the driver's kick panel and see if you can find a connector where the wires go into the door. If you pull the connector apart and the doors lock then you know it must be one of those wires.
Phil.
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