older vehicle, single door unlock

Vehicle: 1989 Chevy S-10 Blazer 2-door. Came with factory power doors. When you unlock one door, you unlock both. I'm wondering if it's possible to wire it so that the alarm disarm only unlocks driver's door, yet the factory switch locks/unlocks or the "door lock on IGN" feature locks both doors as normal? (EDIT: it's "door". not "dor", dummy. Now go find coffee...)"Always listen to experts. They'll tell you what can't be done, and why. Then do it. - Robert A. Heinlein"

I could be wrong, but it sounds like you have five wire aftermarket actuators in each door. You would need to control just the motor legs of the driver's door lock actuator and temporarily disable the signal from that actuator to the door lock control module. Without seeing what you have in front of me, I can not tell you what colors to tie into, cut, and wire to relays. You will need to use a meter and test each lead going to the driver's door lock actuator during lock, unlock, and at rest. Once you've done that, post your findings here, and we'll be happy to help. the12volt • Support the12volt.com

2 wire actuators in each door, factory. There's nothing aftermarket regarding the doors except the alarm (which is only interfacing with the factory stuff). So yes, guess I'd have to replace them with 5 wire?"Always listen to experts. They'll tell you what can't be done, and why. Then do it. - Robert A. Heinlein"

No, no need to replace them, but from your description in your original post, you described the functions of an aftermarket door lock system that locks/unlocks when either door lock is locked or unlocked.

All you need to do is wire up the driver's door lock actuator. Do both motor legs rest at ground? If so, you'll only need one relay to unlock the driver's door independent of the other upon disarming the alarm. the12volt • Support the12volt.com

If both wires of the actuator rest at ground, find the wire on the driver's door lock actuator that only shows 12V+ when unlocking, then cut it and wire it into an SPDT relay as shown below.

 

the12volt • Support the12volt.com

The 89 2 door Blazer is a "5 wire" system. The two 2-wire actuators are wired in parallel. Both wires rest at ground at the LH switch, and "pass through" at the RH switch. The 2 wires for the LH actuator run all the way across the truck, and are spliced to the RH actuator's wires in the RH door harness. To install progressive door locks, you will need 3 relays. The LH door harness breaks-out of the sheet metal above the fuse box. Open up the harness here and find a Lt Blu (All Lock) Black (Passenger Unlock) and Grey(Driver unlock). There are two black wires. One is chassis ground. The other is unlock. You need the unlock Black. It will be the one that goes +12V when the Driver switch is in Unlock. Cut these 3 wires. At each of 3 relays, connect the LH door side of each color wire to pin 30. The harness side to pin 87a. 87 and 86 to constant +12Volt. Pin 85 is the (-)trigger to your alarm, RS, or RKE. Lt Blue = Lock, Gry = Unlock, Black = 2nd Unlock. I'm pretty sure I got it right. I'm looking right at a GM wiring diagram, and have worked with this model truck for over 20 years. But you should try to get a hold of a factory diagram too, and go over it until you understand what needs to be done.

Outstanding stuff, Dave. This is exactly what I was looking for. I am having a weird problem with the factory arrangement. I have two brand new switches installed, but am getting intermittent ability to lock or unlock. No rhyme or reason to it. I understand this is a known issue with GMs but I haven't found any cause for it."Always listen to experts. They'll tell you what can't be done, and why. Then do it. - Robert A. Heinlein"