On the rear there is a copper pad on the section that runs along the width of the boot (the latch conects here too) these can start to get a film on them which stops the contact being made, get some 1500 grit glasspaper and clean them so there bright copper. Also worth doing this to the 4 pins in the boot which connect to the pads.

The front pin switch is a big block near the chassis plate. Its more than likely that the alarm fitter would have put another one on somewhere but it will be on the slam panel somewhere.

Chances are the alarm box will be under the drivers area (above the pedals) its just a black box saying clifford.