If I'm reading it right, your intention is to install the tachometer equipped cluster into a diesel powered truck (and that truck is an M1031) - correct?
I just looked through all my CUCV technical manuals and could find no reference to a tachometer in any service/repair/parts sections. Also checked the schematics sections - none of the wiring diagrams had any indication that these truck were equipped with tachometers. I can't say for sure if this applies to the M1031 - all my CUCV manuals are broken down into two vehicles types; M1010 & all except M1010.
Connecting a tachometer to a diesel engine is not as easy as it is with a gas powered engine. This is due to the lack of any pulsed electrical signal - which any tach requires to provide a variable indication of engine speed.
The fuel/air mixture in the combustion chamber of a diesel engine is ignited by heat of compression. No spark is used.
With a gas powered engine, the F/A mixture is ignited by a timed spark. The frequency of that spark varies with with engine speed. So if the trigger lead of a tach is connected to the primary ignition circuit, that pulsed voltage signal provides the tach with an accurate indication of RPM.
So, since a diesel has no pulsed ignition source for the tach to tap into (to sense engine speed), things become more involved. The required trigger signal must be generated in some other manner.
To run a tach off a diesel requires the installation of an additional component - one that will generate a 12 VDC signal that approximates engine speed. AFAIK, there are three commonly used methods to do this:
1. Locate an OEM vacuum pump that is equipped with an internal tach drive - very rare.
2. Install a Hall Effect type sensor that can track the rotational speed of an external component (e.g. the harmonic balancer or the flywheel/flexplate)
3. I believe that there are alternators available that can generate a pulsed output. Problem is they were only made available in later model trucks and to get an accurate indication of engine speed requires some involved modification.
This is just what I know (or think I know) - and should not be taken too seriously. I sincerely hope that someone else - that knows more than I - has a better way to install your tach.
BTW - when you have some way to power the tach come back and someone will provide the wiring diagrams for you.
