Did it my 86 in about 30 min now do have some proficiency removing the instrument cluster doing odometer repair and blower motor replacement.

Remove the Instrument Cluster by popping off the two gauge blanks and the cover for the light switch, held in by four screws. Then unplug all the wires flip the panel over on it's back and unscrew the big clock. Take a small screwdriver blade and gently pry the large clock off the little posts and remove it by lifting straight up. Install the plug where the clock reset button went, and then guide the tach into place and firmly push it onto the posts where the clock went. Install the screws in the back of the tach and you are ready to install it back in the car. The red white wire goes on either of the top two terminals on the Tach.

On the mini clock, pry off a blank, install the three rubber feet and push into place. If you got the harness with the tach and clock you plug one end into the back of the Tach and the other end into the mini clock. Red Blue goes to the terminal that is insulated, brown goes to the back terminal of the bulb, and black goes to chassis. Snap on the gauge face, reinstall the instrument cluster and check it all out. If you did not receive the small harness, install a black wire to chassis (Center of the Console), splice into a brown wire in the center of the wiring harness and run it to the blub. And run a wire to constant power over on the fuse panel so the clock runs all the time.

That is all there is to it.

Good Luck and Enjoy,

Paul

PS: Now you will want the 5 bar oil pressure gauge, nice add on also.