I had a nightmare with my Veto. Finally ripped it out a couple of weeks ago and bought a new System 3 off ebay (£130). Very easy to fit, took me an evening. You'd need a soldering iron, solder, heatshrink and some tape.
If that sounds brave, believe me I was terrified when I saw the number of wires, but you only need to connect about 12 of them and your old alarm wiring provides all the contact points.
Cheers,
Ali