Disco 2 Rear door light switch?

Hi, I've searched but can't find the right terms....

Just replaced lower rear door (tailgate) hinge and was hoping it would solve another issue. Sometimes the alarm thinks the rear door is open and when I set alarm it toots the horn, my only option is to resest alarm, give the back door a good slam and set alarm again.
Where is the sensor which tells alarm that back door is slightly open?

Thanks all,
Neil

p.s. just fitted egr plate, should have done it years ago!

Probably the microswitch in the rear door lock module. It'll be about £60-80 to replace the whole lock module... so you may wish to live with it!