As per previous advice I decided to get the Thatcham Cat2 immobiliser fitted by an expert as potentially a nightmare if wired wrongly. Ultimately I'm pleased I got someone who knew what they were doing as for the price paid the chaps appears to have done a professional job and it working perfectly well since the install a few weeks ago.
However, I've decided to fit the alarm (and microwave sensor) myself as a bit of a learning project and safe to say it's been somewhat interesting

I seem to be about 95% of the way there but I just can't get the blessed thing to work 100%. Despite numerous wiring checks/double checks and triple checks I still can't figure out what I'm doing wrong.
Just to check my understanding can anyone please confirm;
1) I originally fitted a central door locking kit (you know the ones, circa £20 and simply a push/pull motor/solenoid attached to each door). Using my multi-meter it appears that the lock/unlock is a 12v positive signal to activate. So am I right in assuming this is a "positive" door locking system?
2) Assuming I have a "positive" central door locking system I have therefore have set the jumpers on the AN700 main alarm control box (
http://www.ebay.co.uk/itm/121219616543) to reflect this. (i.e. The jumpers on the AN700 are default set to accept negative input pulse so I needed to change to accept positive input pulse.
The primary problem that I am facing is that I cannot get the central door locking system to reliably set and unset the AN700 alarm. It seems to work for a period of time and then stop. Essentially the alarm accepts the input pulse from the lock/unlock pulsed on the central locking via two wires - one to accept the lock/set alarm and the other to accept the unlock/disarm alarm. I'm sure the problem is here somewhere but all my continuity checks show there are no fault wires (I've even replaced both the wires to 100% confirm this)
What is particularly odd is that the alarm also came with a 3rd (brown) wire for the rare scenario whereby only a single wire is used for the central locking system. If I ground this wire (simply touching to the chasis) then the alarm sets and unset EVERY time and without fail.
I'm hoping the above males sense to someone as I'm totally baffled and my it's really bugging me. However, I'm determined to find the cause of the issue - if only for peace of mind (I appreciate that alarms add little real security to a determined thief).