Why would an 81 Porsche 928 automatic only run while in Park or Neutral?

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Do you mean the engine will only run in park or neutral or the engine will only turn over and start in park and neutral?

it sounds like the neutral safety switch is bad or out of adjustment. If they use one and I dont know the location if that is the case.

Because there is an electrical short within the

neutral safety switch that is interrupting the ignition. When you're in a gear other than the two referenced, there is no spark as a result. Car dies.