How can i fix my Ford fiesta 95 plate alarm?

When the alarm is set using the key the alarm arms itself as normal. But when opening the tailgate the alarm goes off. Normaly one of the two microswitches should bypass this but appears to be faulty. One microswitch is on the tailgate latch and the other is on the end of the key barrel.

The one one the key has 2 wires from the switch and the other microswitch has 3 wires !! Does anyone have any ideas what these two do ?? Many thanks.

Paul
January 2010