I have a great in-dash tach that I am installing in my insanely awesome F150 to increase it's cool.

Just letting you all know how awesome it's going to be.

 

Lol Well sounds like you are excited about it which is good at least!

 

*sigh*
Okay. So the tach is awesome, looks awesome and is in mint condition. The harness that came with it is in pristine condition and has no chipping or broken circuits. I installed it perfectly and everything works as it should.
Except the tachometer.

When I plug in the connector, the tach will jump but not move with the rpms. I am disappointed but I figure it cannot possibly be that hard to find the reason it isn't working. It is a tested part so I know it's a good gauge. The connector has two empty slots so maybe there is a pair of wires under the dash that are taped off?

 

The green and yellow wire under the hood coming off the coil should be the one I run to the tach.

 

I think the circuit isn't compatible with my truck. It was for a Bronco anyway. So I have my original circuit back in place and now I need to know which connection in the back of the tach goes to what.
I have "C", "8", "G" and "B".

Part number EOTF-17360-Y on the back and EOTF-17B316-A on the front. It is a perfect fit so I know it will work for my truck so I'm going to straight wire it if I can figure out what connection goes where.
"C" is to this ignition coil, "8" is the secondary ground for an 8 cyl engine, "G" is the primary ground, and "B" is the 12V power supply -connects to a "hot in run" 12v source.