dingla your best off getting yourself a ford TIS disc off the net off a torrent site. should have all the wiring diagrams you need.

Are you fitting a new alarm later??

Do you want to retain Passive Anti Theft System??

Non aircon???

what features you want determines what you keep.

you should be able to keep the vast majority of aux circuit wiring eg lights, radio, and all that crap.

Also you can keep central locking and standard ford alarm as its independant of the PATS.

If you want to keep the PATS then you need to keep the ECU. On the ford focus the PATS operates through the chip and transciever on lock barrel.

The signal if its the right key earths the fuel pump relay trigger circuit and earths the starter motor relay trigger circuit.

so it acts on 2 circuits to immobilise.

Also as PATS is integral to the original EEC V ecu it locks out the ecu so even if you bypassed the 2 relays it would crank etc but not run the engine.

If you wish to remove the ECU (and hence PATS) you will need to reconnect earths to the trigger side of the circuits for both the relays i stated above. You would then need a immobilisor/alarm fitted to ensure it cant be hot wired.