will be either failed / failing solder joint (most likely) or micro switch failing in the door lock. If you have DIS then you will know which door is causing the issue, but if you don't have DIS then it could be any of the four doors, the tail gate as its own portion of the display
most likely is the drivers door, does the interior light come on when each door is opened ? this may help to pinpoint the failing lock
The locks area PITA to remove, taking about 3 hours each lock to remove and refit, plus the time to repair the lock (reflow joints / fit / clean new micro switch)
if you can pin point the faulty door it would be worth buying a second hand lock, doing the refurb on it and then changing the lock assy over
cheers,
Paul
Even the driver door LED indicator is now flashing when locked which I assume means the immobiliser is back up and running (all doors do lock). But this can't be right?
Could have been in a time warp. The picture with the boot open on the DIS is taken AFTER the one showing OK on the DIS.... Are you sure you got your statements the right way round? Look at the time on the left clock.
It depends on what the original fault was, if it's the tailgate switch which was faulty and that you have now disconnected, then depending upon the wiring it could that open circuit = closed, so as far as the dash is concerned, the tailgate is shut and hence the alarm is set. If you short out the two wires in the plug then this will probably result in the dash indicating the tailgate is open.
I don't have a wiring diagram handy so unable to check but I do know that the front service flap operates in the same way.
The operation of the door locks is much more complex.
Thanks for posting the pictures, these are a useful reference showing the wiring and layout of the interior components.
Ok the led in the door indicates everything is set correctly for the alarm. The immobiliser is permanently on when the key is removed from the ignition and deactivated by the key when inserted into the ignition. So your alarm is activated when the car locks, if the LED is either on constantly, flashing at an unusual rate or off. In your case it does mean the alarm is not enabled. By leaving your dog in the locked ( normally alarmed ) car the interior monitor triggers the alarm and by pressing the button on the B pillar you only deactivate the interior sensing the rest of the car would be still alarmed if all working correctly. Reconnect the lead to the tailgate lock and roll forward the "parcel shelf", ensure the luggage lamp is working, now close the tailgate properly and lock the car. Is the luggage lamp still on? This indicates a fault in the lock assembly and it needs to be replaced with another known good one. The lamp staying on will also kill your battery surprisingly quickly, so I would carefully remove the unit and take the bulb out until the lock is replaced. Another way to test the tailgate lock is to close all the doors and service hatch, lock the car then close the tailgate, if everything working correctly the indicators will flash. No flash need new lock. Best way to close the tailgate is to lower it by hand and when the lower edge is level with the top of the reversing lights let it drop.