Some of the early cummins had a tach pick up on the back of the alternator

 

Is there anyway you could tie it into the original crank sensor? I have a 4l80e with the compu-shift on it and the compu-shift harness has a tach signal wire I can use but not sure where to put it to get the signal.

 

dragging up an old post.....Mech2161, did your setup drive a factory dash tach or an aftermarket? What make/model/year truck? REason I ask is this....I tried the same setup as you suggested for a signal, and it doesn't, or hasn't for me anyway, worked for the 97 GM factory gasser tach. I figure I'll just get teh Dakota Digital dsl-1 box unless someone has any other suggestions. (I'd prefer to keep my factory tach)

 

because a GAS tach runs off of your ignition usually. Diesel rigs are usually more of a pain or were in the past at least, because no ignition.

 

i recently tried to do this set up on a friends pulling tractor, but i cant seem to get it to work. i have tried 3 sensors, 2 modules, and 2 tachs. do you have to use the autometer sensor or can you use any magnetic speed sensor? is there any other ideas to try?