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The red wire is to positive
The black wire is to ground
The green wire is to the tach
TACHOMETERS WILL WORK WITH FACTORY GM POINTS OR FACTORY HEI IGNITION.
WHEN USING AN AFTERMARKET IGNITION SYSTEM LIKES MSD, ACCEL, PATRONIX, ECT.
A LOT OF THESE SYSTEMS GENERATES HIGHER OUTPUT VOLTAGE TO THE TACH LEAD THAN WHAT A FACTORY GM TACH CAN HANDLE.
FACTORY GM TACHS CAN OPERATE ON VOLTAGE RANGING FROM 11.2 TO 14.7
MOST AFTERMARKET IGNITION SYSTEMS GENERATE OVER 18 VOLTS.
YOU WILL NEED TO BUY FROM THE MANUFACTURE OF YOUR IGNITION SYSTEM AN ADAPTER TO LOWER THE VOLTAGE TO THE GM FACTORY VOLTAGE.
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