It kills the fuel pump when you are in a accident so the pump does not keep feeding the fire/engine/spill, etc.
If your wife backs into a light pole at the mall she can trip this switch and the car will not run, as a random non what you asked example.


sdsilvere-what year is your truck?
How many miles are on it?

 

where is the switch located?? also how hard is it to replace crank pos sensor on 1998 disco... it seems like its gonna be pretty hard to get my hands in there. any tips?