Originally Posted by Diesel Junkie

The crank position sensor tells the on board computer the engine is turning, and that is the logic used to enable the field for the alternator.... Pretty lame design if you ask me... but you can check this by checking the exciter wire from the computer.

Mine went bad about a year ago... took a while to figure out. I Should not have been so oblivious about it, because my tach died at the same time too.

Originally Posted by pulltilbroke

Hey Wanna whats 'OP' mean