Wiring for tailgate sensor - door-ajar light stays on

Could anyone tell me what colour wire in the tailgate loom on a Mk1 Focus hatchback operates the door-ajar sensor? The light on my dash won’t go out!

And could anyone offer advice on how to test and repair the wire? (I can access the wires in the ribbed rubber tube at the top of the tailgate but would guess I’d have to remove a trim panel somewhere to unplug the loom, so I’d be grateful for some pointers!)

I’ve tested all door striker plate sensors with a supposedly good unit but the door-ajar light on the dash still stays on, so I’m guessing the fault is in the tailgate. However, the tailgate doesn’t appear to have a plunger-type sensor like the doors, so I’m thinking the fault must be a broken wire in the tailgate loom.

(I read on this forum that the constant opening and closing of the tailgate can make the wires brittle.)

I’m not an expert on car electrics and have only a very basic circuit tester, so any guidance would be much appreciated!