I've swapped a 4bt into my '91 Dakota. I want to hook up the factory (indash) tach. I've tried using a wire off the alternator through a headlight switch (for adjusting RPM) then to the tach output wire that was on the computer. NO WORK! I was wondering if I could use a crank sensor instead?
Any info would be appreciated.

 

The computer on the Dakota probably used a spark signal to run the tach, out of luck with a diesel. Sort of doubt the signal from a crank sensor would be compatible with the gasser computer.
Might be easier to use one of these, small, cheap, easy to install and very accurate
http://www.tinytach.com/tinytach/diesel.php

 

I've eliminated the computer completely. It picked up a signal from the distributor using a "Halls effect" sensor. I've thought about fabricating something using those parts. Any ideas?

 

The 12v uses a hall-effect sensor on the front of the engine on the harmonic damper. It's a 5? volt trigger that fires once per rev. You may have difficulties if the tach was driven off a dizzy. Is the polarity the same?

brandon.