Cobraman

I recently bought a 2000 W Mk 1 Galaxy 2.3 auto and among other minor things, the high level brake light wasn't working due to receiving no power from the circuit. I piggybacked a new wire from the offside brake light, though it was really difficult feeding the wire through both the D pillar and the top of the tailgate. I used some stiff copper telephone wire as a feed through and eventually got there and now have a working HL barke light. However now the electric tailgate lock won't work and I can't get in the back. Surprisingly, it won't even open manually on the key. Obviously my prodding and pulling has broken another cable to the lock motor. but can anyone tell me how to get the tailgate open? I can't get the trim panel off from inside as it has screws around the edge and the two access panels for the tailgate light bulbs don't seem to access the appropriate part of the loom for the lock motor.

I understand this is a fairly common failure. Mine won't engage 4th gear and shows "Speed sensor" as the fault code. (New sensor made no difference.) Before I stump up