Too clever these locks, lock and unlock is achieved by reversing the polarity at the BCM. Im getting a short pulse to the lock which would suggest that the wiring is ok but im wondering whether its looking for feedback on the red or maybe a current feedback protection circuit in the BCM.
I have a new BCM but reprograming looks a bit daunting. Opened the old one up to test the relays but its two boards soldered front to front so its pretty much tamper proof. I know im gonna have to fit the new BCM at some time and get my head around forscan.....Im getting to old for this.

 

Hey Mike,
If you keep telling yourself you're too old for this , it won't be long and you will be !
Challenges and learning something new is part of what keeps us from growing old.
There is so much to learn out there and growing with it is what keeps a lot of us going.

 

Is this extra red wire built into the wiring harness or has someone added it extra.

Remove the right rear door panel and check if that door latch also has this red wire.

Check under the dash for an aftermarket alarm or remote start feature.

Unplug the left rear door latch and check if the latch itself has a pin this wire goes to or not.

Check if this wire has power or ground, check for power both key on and key off.

If the right rear door latch and liftgate latch work correctly you can cross out the BCM.

Post your vin and I can run it to see if there is something special about yours, maybe its not a USA model so has slightly different wiring.

 

Thanks Scott it was Built in Germany, that could explain the difference. So many unknowns, all the doors lock apart from this one but only the driver and tailgate lock electronically. Im going to have to check each lock and switch, the weird thing is that the tailgate latch functions correctly suggesting that a lock signal is being supplied to all the locks. It could be that there's insufficient power to operate all the locks (S332 main gnd ) . I shall do a full investigation and upload the results.

 

Since it was built in Germany post or pm your vin and I'll run it to see how its set up.

 

Hi Scott, been busy examining the right rear door lock, replaced it this morning and that one works fine though there is this mysterious red wire on this side too. This is what I discovered, the locks contain three micro switches, one for the door ajar and two moulded together but only one is used on my model the motor drives gears that are sprung loaded so when the cam hits the microswitch the motor stops but the gears continue till the switch is clear of the cam. On this lock it is a two way switch so when the motor is off the red wire temporarily energised until it passes the cam. As this circuit is bi polarity then the red must be a lock/unlock signal. The new lock I fitted did not have pin 4 but works perfectly well and I left the plug disconnected (linked out door ajar) on the left door. Annoyingly since stripping this down the motor works fine and the micro switches are working so the mechanism must have been stuck with with the microswitch open. Just got to check the rest of the locks, maybe its a mechanical problem .

 

VIN is WFOCU93125KB49001

 

So I guess I dont have access to vehicles sold outside of north america.
Granted you ended up confusing me with what the issue is now.

 

Thankyou, your interest in this query was much appreciated.