Use the wire color code to locate the below connector:

Above the accelerator pedal is a 4-wire plug with a harness that runs down to under the accelerator pedal and to the transmission tunnel. Unplug it, jumper across the two purple wires in the female plug and try to start again.

The member who gave the above info did not say what colored stripes the Pruple wires had on them but jumpering them bypasses the Neutral Safety Switch and you will start in any gear.
The other 2 wires on the Connector i presume are for the Back Up Lights.

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84 300D, 82 Volvo 244Gl Diesel