850 keyless entry into a 740
I spliced the keyless entry system from a 1995 850 into my 1989 745. It's fairly straightforward once you know what you're doing. The locking hardware is all factory, so you don't have to hack up your door panels with a crappy aftermarket system.
This should work with any 7/9 that already has central locking. Essentially you're installing a keyless system for the driver's door, then the 740's factory central locking takes care of the rest of the doors and the tailgate.
What you need from a donor 850:
-Central locking relay. It is almost directly in front of your left knee as you're sitting in the driver's seat, all the way against the firewall.
-Keyless entry control module/receiver with harness. It is located between the glovebox and the end of the dash on the passenger's side. Take the glovebox out to access the unit.
-Remotes. These don't have to be from the car that you take the module from, but that will make it easier.
What you need from a donor 740:
-Rear driver's side lock actuator. I used the early style "L shaped" one (pictured) instead of the door latch mounted ones from the later 740s and 940s because it is easier to work with.
-Front passenger's side lock actuator bracket. The brackets are different for the front and rear doors.
-Front passenger's side lock actuator linkage. Get both metal rods and the plastic pivot mechanism that connect the lock actuator to the lock pull at the top of the door. Take all the clips that hold the rods together as well.
Other stuff you need:
-Wire, electrical tape, blade style connectors, crimp connectors
-Zip ties
Putting it together:
Mechanical
-Remove the front door panel. Also remove the knee bolster, pedal cover, and side panel in the driver's seat area.
-Install the lock actuator. Swap the bracket from the front passenger door onto the actuator you got from the rear driver's side door. The bracket is screwed into the door with three screws (holes pre-drilled).
-Remove the door latch (two Torx bits). Also remove the small Phillips screw that is behind the latch to loosen the mechanism in the door that is attached to the door latch.
-From inside the door, disconnect the clip that connects the lock pull rod to the latch. Leave the lock pull rod resting in its hole in the latch mechanism.
-Reverse the direction of the linkage you pulled from the donor 740. Since it's going on the driver's side, unhook the rods and basically flip the assembly so that it's a mirror image of the passenger side. It should look like this (below). Compare it to the picture of the linkage at the beginning for reference.
-Push the linkage assembly up through the gap in the door. You can look through the largest hole in the door to see what you're doing. It's tricky. The top of the uppermost rod in the linkage has a hole in it that will fit on the lock pull rod. Once it's hooked on, put the clip back on (very tricky). The lock pull rod should now be secured to the locking mechanism and the linkage you just installed.
-Secure the rest of the linkage. There's one screw for the white rotating thing in the middle.
-Clip the smaller rod to the hole in the lock actuator.
-Replace the door latch and the small Phillips screw underneath it.
Electrical
The keyless entry control module/receiver has four wires coming from it.
Red: 12V at all times
Black: ground
Green/yellow: signal wire to locking relay that controls lock/unlock cycle
Yellow/violet: 12V with key in ignition
The central locking relay has a legend on it that shows what each post does.
ATR: green/yellow signal wire from control module/receiver
31: ground
M+: red/white wire from lock actuator
M-: red/blue wire from lock actuator (one of these is the lock wire, one is the unlock.)
30: 12V at all times
15: 12V with key in ignition
Run wires from the lock actuator in the door to the relay. I attached the relay to the receiver and mounted both above the brake pedal, so use enough wire to get there. Stringing the wire through the rubber plug on the side of the footwell is tricky. I pushed a small screwdriver between the rubber and the wires it protects so that there was just enough of an opening to slip the locking/unlocking wires through.
Connect the relay to the control module with the green/yellow signal wire.
Connect the constant 12V supply to both the relay and the control module. I spliced into the hot wire that goes to the headlight switch.
Connect the 12V with key in ignition. This is optional- it doesn't affect the operation of the unit if you don't connect it, but you may need it to reprogram the remotes (if the remotes didn't come from the same car as the receiver. More on that later). There are plenty of keyed 12V wires under there, so you might as well connect them.
Connect the grounds to both the relay and the control module. There is a nice ground box in the driver's footwell.
Test it out! Make sure the driver's door is closed (otherwise it can't lock). Mount the relay and control module, zip tie all the wires up so they don't rattle, and button it all back up.
I found that the remotes have a 10-15 foot range. The higher you mount the receiver the better (also away from metal), so you may get more range if you can place it higher up in the dash.
Note:
If you have to reprogram the remotes from match the control module, here is the procedure:
-Switch on the ignition to positions I or II 5 times within the space of 10 seconds, and leave the ignition on the 5th time.
-Within 30 seconds, press either the "LOCK" or "UNLOCK" button once on the transmitter. All the transmitters must be reprogrammed within 30 seconds.
-Switch off the ignition.
-Check that each of the transmitters functions properly.
