C is Common

NO is Normally Open

NC is Normally Closed

12v goes to Common

If the switch is not tripped due to impact ( NORMAL ) then the voltage will go through the switch
 and appear at the Normally Closed contact. This is where you wire to the pump ( You should actually 
use a relay as the inertia switch is probably not designed for high current long term use)

If the switch is tripped then the NC goes open killing the power. The Normally Open contact closes.
 This is a newer switch so it is equipped with the NO switch to light a bulb in the dash to alert you
 the inertia switch has been tripped. Older Fords don't have this feature and are thus a two contact NC switch.