Hi,
We just had this problem on our daughters but fortunately have a retired Jaguar/Aston electrical designer in the family.......
Firstly you say the boot is jammed so I would assume your garage have managed to open the boot to establish that it is the harness wiring or have they just assumed the problem which is a well known very common fault........
To open the boot manually there is a simple finger trigger on the bottom lefthand side of the tailgate lock when looking at it from inside once you have done the assault course of climbing over the seats to the interior. See pictures
If you have though first checked everything else works ie lights etc and you do not have a cluster warning of open door on the sppedo and it is just the boot failing to open on the remote/finger latch then all you need to do then is remove the rear tailgate trim, remove the connector that is attached to the tailgate lock opening/solenoid and check to see if you have a 12v supply on the purple and black wires when you press the remote or finger latch...................
No 12v then it is a break in one of the wires black or purple inside the boot convoluted rubber grommet more than likely. If you have 12v then the lock solenoid has failed........£18 and 5 minutes to replace..........
If a loss of 12v but everything else works then detach the convoluted grommet from body and tailgate and see if the car has had a previous repair as ours had had 3 years ago by a main dealer........however the black wire had broken off where it had been soldered and covered in heat shrink.....
It seemed pointles changing all the wires again (cost over £100 main dealer 3 years ago by previous owner) for the sake of a single one wire that had lost continuity albeit we do have a vacuum with a mains lead silicone cable wire and it is unbelievably flexible so I would agree a sensible consideration as baglady mentions..........that said we just threaded a new black piece of wire through, resoldered and new heatshrink at each end....job done
As with most electrical jobs identifying the exact location/cause takes a lot longer than the fix, but just make sure you establish the fault is the harness and not the actual electric lock mechanism.......
Personally I would look for a local alarm or radio installation person as they will have all the right tools and experience but there is nothing difficult in repairng this.......
WE as in the worker (electrician) and his boxed apprentice!!!!!!!
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