Short answer is remove the plug and install a new pressure sending unit and plug in the connector. It should be a standard 1/4in pipe thread.
Long answer is those sending units have a history of splitting open and sending all you oil out over the road and if you don't catch the pressure needle fluctuating then the sound of an engine running without oil will.
This happened to the previous owner of my 92 YJ and it trashed the engine. As a test I put a temporary plug in along with a few quarts of oil but the engine was too far gone. The sending unit was spraying out about a quart every minute.
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