'95 grand prix not firing, need location of possible causes

my fathers grand prix just recently died on him after running fine for more than 12 years. there is no longer a spark on any piston and what are the chances that all three coil packs went bad at the same time? so i have narrowed it down to 2 possible causes. 1: the computer is fried 2: the C.A.S. (crank angle sensor) came disconnected or needs replacing. the only issue is i cant find the sensor anywhere. could you please let me know where the c.a.s. is? all i know is its in the back end of the engine.

any other thoughts can be helpful.

finally got it running. apparently a heat sheild fell off in the back of the engine and we think that it was shorting the ground.