I had a similar problem with a L Reg Mk 1 Mondeo, where the alarm would set itself going everytime I started the car; It turned out to be the bonnet switch. Each time the car was started the bonnet would flex on it's mountings and set the alarm off. This switch is different to all the other alarm micro-switches, in so far as it does other functions to do with the alarm system. All I did to fix it was to find the wiring going up to the switch, cut off the offending switch and join the two wires by baring some of each conductor wire and twisting them together finishing off with some insulating tape. The switch is located st the left-hand side looking at the engine (off-side or drivers side) and has a rubber boot protection. Bascially, the contacts in the switch wear out through vibration, the bonnet constantly flexes when driving.
Martin, March 2008
