Dennis,
Standard Ford products of the era ran current to the ignition through the tach, not so with the Pantera. Your mechanic is mistaken, but it is an honest mistake, one I would make myself if I didn't know otherwise. The Pantera's tach is connected to the negative terminal of the coil. Power supplied to the coil is connected to the positive terminal.
When the engine cuts out, is the car moving or parked?
George
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