I've got a question and maybe some of you have ran into this. For my factory tach plug it has 2 black 18ga wires an orange 20 ga and a grey w/light blue tracer 20ga. I have already looked at the sticky "let's screw up your column". It says Black 18ga Orange 20ga red 18ga and grey w/ light blue tracer 20ga. Other than tracing the whole harness out can anyone tell me which black is the "red" wire?

 

If your connector is still intact, the black wire on the end is ground, and the black wire that sits between the orange wire and grey wire is the "red" wire. Take a look at these stickys for clarification:

Isspro tach wiring diagram:
https://www.dieseltruckresource.com/d...58&postcount=3

Factory tach harness diagrams:
https://www.dieseltruckresource.com/d...d.php?t=185725

The connector was removed in mine so I had to use the multimeter to tell which black wire was the switched power.

 

Thank you. I pulled my head out of my rear end and used a test light to see which was which.

 

Sometimes, one may have to skin the insulation a little to see the actual color.

 

I tried skinning it and it was black all the way through but got it hooked up and the gauges are working nicely. Thank you guys for helping out