Mitsubishi Shogun 2004 shogun 3.2tailgate door won't unlock.

Well kept and serviced vehicle 82000 miles. Tail-gate door won't unlock, noticed an electrical over-heating smell. Tried several times locking/unlocking central locking system at driving door lock with no effect. All 4 other doors lock/unlock OK. Tail-gate finger handle has spring pressure so unlikely to be a seized/rusted return spring. The key will not turn in the tail-gate lock which seems to be seized. I presume this is an electrical/solenoid failure in the tail-gate lock mechanism but can't access it.