Just picked up a 92 12 valve 5 speed with a 78 body on it. It needs some work but its going to be an interesting adventure getting this truck to the point I want.

Anyway im working out the bugs to get it ready for inter-provincal inspection here in alberta (bought it in BC), and I am in no way great with anything electrical Ive looked up wiring diagrams for the current RPM gauge i have in the truck which is a Isspro R1640-4, followed the one provided here Dodge Diesel - Diesel Truck Resource Forums - View Single Post - Questions about hooking up a Isspro tach with no luck still. I found the harness that it plugs into just no response from the gauge. The needle does move or surge whatever you want to call it when i shut the engine off. I read that you can fry some things hooking it up wrong soooo hopefully that isnt the problem.
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Yes its a absoulute disater of wiring but let the fun begin!

Thanks

Chance

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.