Join Date: Jan 2013
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I just recently finished my 4wd conversion on my 84 crewcab. I used the same Isspro tach R16040-4, I had this tach on my 89 motor, with the magnetic pick ups on the harmonic balancer. But I converted everything over to my 93 cummins 4wd donor.
Anyway I didn't want to have to buy a new tach. So I initially tried wiring the tach straight into the factory 93 plug. I got the same results as you. The tach needle would just jump a little when the ignition was turned on.
SO I bought the conversion harness from Geno's. I then tried it again, this time with the white wire, and the filter/signal amplifier. Works perfectly.
It does appear that you have the Geno's conversion wiring harness. Double check the wires coming off the back of the tach...to make sure they are going to the right colored wires. And then hook the wiring up to the factory pug.
The danger in the wiring is if you accidentally cross any of the wires when plugged into the factory wiring connection. I just removed my battery cables to make sure there was no power in the system, when I hooked, and unhooked my wires....better safe then sorry.
1984/93 Dodge Crewcab, W350, 1 Ton SRW, long box, 350K Km's, hydroboost, 366 spring, fuel pin to deep side, 14cm housing, Piston LP, PS IC, Isspro Boost, Pyro and tach, NV4500, 29 spline NP205, 3.54's.