I have not read of anyone posting this particular problem.

You might apply your Voltmeter to the Battery Terminals an have someone turn on the Glow Plugs and see how far the Voltage Drops. The Voltage should not drop much more than 11-11.5 Volts.
May not be your problem but worn Shifter Bushings can mimic a bad Neutral Safety Switch.

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84 300D, 82 Volvo 244Gl Diesel