Tach currently not working.

What are the functions of the 2 wires attached to the tach?
I see a dark blue and a yellow with black tracer.

Trying to follow routing through firewall and couldn't follow it in the manual wiring diagram.

Thanks

the diagrams at www.mymopar.com might help. there would need to be the hot 12V power in then the lead to the coil neg primary terminal (for the sensing function) then a wire for the bulb (& 4th, maybe a dedicated ground connection). EDIT I would assume the dark blue is the switched 12V power in & the yellow with black tracer is the sense wire (as yellow/black is the color of the wire from the ECU to the coil neg primary)

There's a grey wire that is on the engine side of the bulk head connector that is part of the windshield wiper plug or is it the reverse back up plug? that connects to the coil to make the tach work.