Ref my 75 F-150: The aftermarket tach clamped to my steering wheel column died. I have no clue what wire goes where. I found a thin green wire not connected by the power steering pump.

 

Thin green wire goes to the coil. Don't recall off the top of my head which side. Also have a red and a black for power. Hope this helps. Maybe that wire broke? Other end of it might still be attached to the coil so maybe a simple splice will get you back in business.

 

I found another screw up.........The horn got rewired bypassing the horn relay. When I tear the dash apart to install LED bulbs and find the wire to the blower, I'll look for the wire going up the steering column....and 12 volts.
I'd send pictures if I could find what to click on.

 

 

Good News. The thin green wire was connected to the coil. The coil is hiding under the air cleaner. All is well. The tach works fine.

My next project is replacing the dash bulbs with new white LED bulbs.....&....repairing the dead wires to the a.c. blower switch.
They are wrapped in tape all the way to the small fuse panel. That involves removing the fuse panel. No clue which fuse feeds
the orange / yellow wires.