Hi firstly check if the lock actuator tries to move..put your ear against the tailgate and listen for a click or buzzing noise as you push the remote. You can remove the trim panel and look in to see if the locking mechanism is intact, using a multi meter check if voltage is getting to the actuator....If your getting voltage to it and it doesn't move get a replacement from a scrap P38....just take the old one with you to confirm it has the same pin plug as yours before you buy it or you could look for one on Ebay.
