I wanted to point this out in case it might be of use to someone. Design Technology makes a unit called Tiny Tach that is a simple install on most any diesel. I installed it on my 4JG2 and it works well.

In my situation, my Trooper had a petrol tach that was made to work off the ignition coil's 12v impulses. My diesel has the reverse where the tach pickup on it sends ground impulses. I couldn't figure out how to bridge that gap, so opted for the Tiny Tach.

(I didn't go the route of picking up a tach from an older diesel trooper as I couldn't find one. That would have been the more ideal path)

Hope that's of use to someone.

Paul