Chevy/GMC Truck 1967-1972 Classic Instrument PDF Installation Manual

Determine Tachometer Signal STANDARD POINTS & CONDENSER SYSTEM Connect the negative side of the coil (usually marked as “-“) to the signal wire for the tachometer. GMC – HEI (High Energy Ignition System) Connect the “TACH” terminal on coil side of distributor cap to the signal wire for the tachometer.

MSD (Multiple Spark Discharge System) Connect the Tach post on the MSD box to the signal wire for the tachometer. If the tachometer does not
respond, your MSD system may require a MSD Tach adapter. Part No. 8910 or 8920.

VERTEX MAGNETO SYSTEM Connect the “KILL” terminal on side the of Vertex magneto body to the signal wire for the tachometer. An external adapter such as an MSD “Pro Mag Tach Converter” #8132 may be required.

ACCEL IGNITION COILS Connect the negative side of the coil to the signal wire for the tachometer. CAUTION! Some Accel ignition coils require the tach signal wire to be connected to the “+” terminal on the coil! PLEASE carefully read Accel’s instructions before connecting ignition coil.

MALLORY IGNITION Connect the negative terminal side of coil (usually marked as “-“) to the signal wire for the tachometer. IMPORTANT! Some Mallory ignition systems may require you to adjust the tachometer selector switch to be set at the 4-cylinder setting (rather than the 8-cylinder setting). The selector switch is located on the backside of the tachometer case.

ECM TACHOMETER SIGNAL Signal comes from the computer. When using this type of signal, you may need to set the tachometer to a 4-
cylinder setting regardless of the actual cylinders on the engine. Signals below 8V amplitude require the use of either the SN76 tach adapter or a 1K .25W pull-up resistor installed between the signal and power post of the tachometer.

MULTIPLE COIL IGNITION SYSTEMS A tach adapter is required for these ignition systems. A tach signal driver such as the MSD #8913, which
produces a 12V square wave signal, is recommended. Please check with manufacturer for your specific application.

Wiring the Tachometer Step 1: Connect switched +12VDC to the pink wire on the 6 pin connector [position F] of the instrument wire harness. Step 2: Connect a ground to the black wire on the 6 pin connector [position D] of the instrument wire harness. Step 3: Connect the tachometer signal to the white wire on the 9 pin connector [position J] of the instrument wire harness. Step 4: Set the tachometer dip switches to the appropriate cylinder setting for your signal. Refer to Table 1 and Figure 3 below. : Some ECM tachometer signals require the tachometer to be set at the 4-cylinder setting Note regardless of the actual cylinders on the engine.

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