I never did it but you can get a start by looking under the bolster, just under the Bulb Failure Relay, there is a three wire connector Black wire with a red insulator on it, Green wire and red wire.
That is the connector that comes directly from the drivers side Stalk.
I believe the Black wire is the nuetral connector and jumping that to one of the other two will Lock and unlock all the doors.
Inside the door, the stalk has three wires , you can take those and run a momentary On-Off-On switch on the armrest somewhere
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'75 Jeep CJ5 345Hp ChevyPwrd, two motorcycles, '85 Pickup: The '89 Volvo is the newest vehicle I own. it wasn't Volvos safety , it was Longevity that sold me http://home.no.net/ebrox/Tony's%20cars.htm