[OAC_Sparky]

If the dome light doesn't fade out then the clicking you hear is the solenoid. It's on the starter (IIRC), it sends power on to the starter, pushes out the starter gear to the flexplate/flywheel and powers the starter.

If the battery was low then you'd hear the clickclick and the dome light would go dim, instrument panel and your radio would fade out (and the time would reset, etc.). If the dome light stays bright then the starter either isn't getting enough current (bad/corroded connection) or the starter/solenoid has a pooched winding and (if it''s the solenoid) not passing enough current or (if it's the starter itself) isn't producing enough torque with the remaining winding.

More likely it's the solenoid if it's still clicking but I don't know if the Focus's starter solenoid is serviceable as it's attached to the starter (IIRC). Some are, some aren't.

I just went through this on my wife's Taurus.