Alarm Issues

I know there are 100's of Alarm issue threads out there but my confusion is just getting worse by reading them.

I recently had an issue with my Rear O/S door mech that failed and required the door being ripped apart and replaced.

I then find out that my alarm has been going off non-stop since owning it from 12o'clock at night! and when it rains.

I have read all the threads and looked at the rear boot light, which goes out once the boot is shut, I have tried all the doors and it seems that the Rear NS Door is not being recognised as being opened on the Dash.

How do I fix this issue whilst on this goose chase?

Seems that car I looked forward to owning has just been a thorn in my side so far!

I live in Aylesbury if anyone is around to help (not a mechanic so not the best at working on cars).

many thanks,

Daniel