What am I looking for here....

[Tiwaz]

Before purchasing a tachometer,
(which by the way if anyone has one for sale with canon connector let me know)
I would like to know if the harness is good so a "Plug n Play" situation would occur.
In the picture is the connector hanging by the windshield wiper motor and two of the wires (27P and 57L) are self explanatory, respectively +24V and GND but the question is:

What would I be looking for on the third (2D) wire with a multimeter....?

Would it be some AC voltage...? DC voltage...? some kind of impedance, how would I know that 2D has what it takes to make the tachometer work...?

 

[FlameRed]

Sorry, I don't see any picture in your thread...

This is of little help to you as mine was a M998 with a 6.2 and there was no harness for a tach. So on the 6.2, there is a sensor on the very back of the engine with two wires coming out of it. The tack connects to these two wires as the data source. Ignition source is important or the engine meter will run up.

Then there is a +24V ignition source needed, and ground, and a source from one of dashboard lights so the tach lights up with the other guages on the dash.

I just used posi-lock tap connectors into existing wiring.

 

[Tiwaz]

Sorry, I don't see any picture in your thread...

sorry.... my bad View attachment Tach Wires definition.jpg