OK guys, I got a tip on another board. Here is what was happening: It turns out that the voltage gauge or idiot light wire (brown) from GM internal regulated alternator supplies a small amount of current, enough to supply power to the MSD unit. The MSD kit includes a diode which I soldered into this line and the problem is solved. The diode will not allow power to reverse in the line and therefore isolates the MSD from receiving power from the sensor circuit.
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