How to Wire a Mallory Tachometer

Most Mallory tachometers are universal, enabling them to operate on four-, six- and eight-cylinder vehicles with a simple adjustment. Mallory tachometers are capable of operating a shift light, which is an excellent addition. The shift light plugs into the tachometer and works with the settable rpm limit pointer. When a specific rpm shift point is dialed in on the face of the tachometer, the light illuminates.

Things You'll Need

• Box of assorted wire connectors
• Quick connect (piggyback) wire connectors
• Shrink wrap
• Source of heat for the shrink wrap, such as a lighter or heat gun
• Wire crimper tool
• Set of wrenches
• Roll of 16-gauge wire
• Voltmeter
• Pliers

Instructions

1. Set the tachometer to coincide with the number of cylinders. Read the instructions with the tachometer. The Mallory tachometer is preset for a V-8 engine. If your engine is a four- or six-cylinder, you need to change the setting. Mallory has two methods, depending on the type of tachometer, to change the setting. One is to flip a switch marked 4-6-8 on the back of the tachometer, or there may be series of three wires, two of which must be cut.

2. Locate a "keyed" power source wire, which means that the power should be present only when the key is on. Look under the dash on either side of the steering column for a large wiring harness connector with the wires coming out of the steering column. Look for the larger diameter, 14-gauge wires from the ignition switch. Avoid any wire that is yellow with a black stripe; this is the air bag wire and probing it could set off the air bag. Connect the black lead from the voltmeter to a good ground. Turn the key on and use the voltmeter's red lead to probe the wires and locate one that has power with the key on and no power with the key off. When the wire is found, mark it.

3. Connect the power wire (the red wire) from the tachometer to the wire just located using a quick connector. Place the connector over the wire and push the wire all the way to the back of the connector. Place the red wire next to the main wire and pinch the cap closed. Place a pliers over the connector and pinch the protruding blade down to pierce the two wires. When the blade is all the way down flush with the top of the connector, close the locking cap over the blade and push it until it clicks in place.

4. Connect the yellow wire, which is the light for the tachometer, to the fuse block. Pull one side of the instrument fuse out of the fuse block by lifting one side up and swinging it away from its terminal. Strip the insulation off the end of the yellow wire with the wire crimper. Twist the wire end until the wires are tight. Wrap the bare wires around the metal end of the fuse. Keep the wire in place around the fuse and use your thumb to push the fuse back into its holder. This pinches the red wire in place on the fuse.

5. Attach the black ground wire to a good ground using a post connector, which is a circular connector made to slide over a bolt or screw. Strip the insulation off the end of the black wire and insert this end in the post connector. Crimp it with the wire crimper. Place the connector under a screw or bolt and tighten.

6. Attach the green tachometer wire. This wire needs to pass through the firewall and be connected to the coil. Look for a rubber grommet on the firewall. This could be where the parking brake cable passes through, or where all the wire pass through on the upper-left side of the firewall. Run the wire through the firewall and over to the coil. It may be necessary to add a length of wire if the tachometer wire is too short. If so, use a butt connector out of the box of connectors. This is a small, barrel-type connector where the end of one wire is inserted into one end and crimped, and the beginning of the other wire goes in the other end and gets crimped.

7. Remove the black negative terminal on the coil using a small wrench. Connect a post connector to the end of the green wire and place it on the negative terminal on the coil. Place the original wire on top of the green wire terminal, install the nut and tighten.