- 1). Connect the temporary external-mount diagnostic tachometer under the hood by connecting the two wire leads to the battery -- the black to the negative ("-") terminal and the red to the positive ("+"). Connect the green lead to the negative terminal on the coil.
- 2). Set the tachometer cylinder select switch to the engine size. This relates to a four-, six- or eight-cylinder engine.
- 3). Start the engine, and observe the display for rpm.
- 1). Program the tachometer to coincide with the engine's number of cylinders. Tachometers have two procedures for programming the tachometer, so read the instructions for your particular model. Most have a switch on the rear of the tachometer, which is either exposed or under a cover. Some have a series of three wires. The instructions will require cutting one or two of the wires if the engine is other than a V8.
- 2). Separate the four wires. There is a red wire (battery +), a black wire (ground), a white wire (illumination) and a green wire (coil -).
- 3). Connect the red wire to a switchable power source either from the back of the ignition switch or the inside fuse box. The power should be off with the key. Connect the black wire to a good ground. Connect the white wire to either the fuse box accessory lights or to the accessory side of the ignition switch.
- 4). Connect the green wire to the negative terminal on the coil. This will required locating a spot to pass the wire through the firewall to get to the coil. A good suggestion is to pass it through next to the harness connector on the firewall. It is held in with a rubber grommet and a common screwdriver can move the grommet out of the way enough to pass the wire through.
- 5). Start the engine, and observe the display for rpm.
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