I went thru the same story here 2 years ago. Get the tach and pay no mind
to all the 18 second, big ass look, car is too slow stuff. So you want to
know what your real rpm are.
The tach has a white wire for lights. I spliced into a wire on the headlight switch so it'll fade with the dash lights as well.
The tach has a red wire for power. I spliced into the wire behind the fuse panel for my a/c. I dont have one anymore so it was free.
The tach has a black wire for ground, anywhere on the body in the car is fine.
The tach has a green wire you need to splice into on your coil. It should be the green wire also. This is where it picks up you rpm signal.
The rest is just finding where you want it mounted and screwing inthe mounting plate.