Alarm Trouble: Boot Not Arming

[V8 Archie]

I've recently had a new rear end as a result of stopping at a zebra crossing. My alarm now beeps at me when I set it. It only ever did this before when part of the system wasn't armed (due to doors or boot being open).

I took it to a dealer, where I was told that on cars of my age (facelifted, but not very late - mine is 1999) there's a button/sensor near the fuel cap that is depressed/activated when the boot is shut properly.

I reckon it's more likely to be something around around the boot catch.

Does anyone have any knowledge that might help track this down?

[Ribol]

Mine(2000) has the switch built in to the boot lock itself for sure, no other switches anywhere else.
As I think you have already worked out, they probably have not connected it back up to the alarm after the repair.