A tachometer is an instrument that measures an engine's speed in revolutions per minute, or RPM. Affectionately known among high-performance car enthusiasts as a “tach,” the tachometer helps prevent drivers from operating engines beyond recommended RPM limits. More subtle, everyday drivers often use a tachometer to help conserve fuel and assist in timing shifting patterns when operating cars with standard transmissions. You can install a tachometer gauge yourself with the proper tools, materials and basic automotive knowledge.
Turn the ignition switch to the "Off" position, and remove the keys.
Raise the hood of the vehicle.
Select the number of cylinders the engine has on the tachometer. Check the tachometer manufacturer’s directions for the correct setting procedure.
Find a location for the mounting base of the tachometer. Check to ensure the position chosen provides the best visibility. Tachometers are usually mounted on the top of the instrument panel or strapped to the steering column with flexible worm-drive clamps.
Check the auto service manual for your car to locate the fuse panel and an available 10-amp circuit wire leading from it. Tachometers require 12-volt power for operation. Also check for the location of headlamp wiring as the tachometer requires power from the light circuit for illumination.
Connect the white wire from the tachometer to the selected lighting wire by splicing the two with a crimp-lock coupler. No wire stripping is necessary for this splice. Place the tachometer white wire on one side of the coupler and the lighting circuit wire on the other, and close the coupling.
Compress the two metallic conducting jaws of the coupler into the wires with combination pliers until the tip of the jaws are flush with the top of the coupler. The jaws pierce the insulation, making the connection between the two wires. Snap the coupler's protective cap over the connection.
Connect the red wire of the tachometer to the 12-volt terminal wire from the fuse box. Splice the connection using a 1/8-inch crimp-lock coupler and pliers. Snap the cover closed.
Place a fender cover over the area on which you are working to prevent scratches from tools and belt buckles.
Look for an access plug that allows wiring to pass from the interior of the car, through the firewall and into the engine bay. Access plugs are not in all automobiles. In this situation, drill a 1/2 inch hole in the firewall to the right of the steering column with a drill fitted with a 1/2 inch steel drill bit.
Install a rubber grommet into the drilled hole by placing the smaller, tapered end into the hole first. Push the grommet into the hole with your thumb until it snaps into place. The grommet usually comes with the tachometer, but you can also find them at hardware and automotive parts stores.
Insert the black and the green wires from the tachometer through the grommet or access plug hole and into the engine bay.
Remove 1/2 inch of insulation from the black wire using wire-stripping pliers.
Fold the exposed copper of the black wire in half, and insert it into the end of the 3/8 inch loop crimp connector. Crimp the end tightly with the crimping pliers.
Locate the automobile battery. Remove the negative (-) battery post clamp nut and bolt with an adjustable wrench. Turn the nut counterclockwise to remove it.
Place the bolt through the looped connector attached to the black wire, and reinstall the bolt into the post clamp. Tighten the clamp nut clockwise with the adjustable wrench.
Locate the engine ignition coil using the auto service manual for your particular make and model automobile. Remove the negative (-) post nut on the ignition coil with the adjustable wrench. Turn the nut counterclockwise to remove it.
Strip 1/4 inch of insulation from the green wire from the tachometer with the wire-stripping pliers.
Insert the stripped end of the green tachometer wire into an 1/8 inch looped crimp connector. Crimp the end tightly using the crimping pliers.
Install the 1/8 inch looped connector attached to the green tachometer wire over the negative post of the coil. Tighten the post nut clockwise with the adjustable wrench.
