6 oil pressure sender light

Your dilemma has me perplexed, So I went and took photos. The metal plug is what was in the pump when it came out of the box. The brass is a 3/8 npt elbow.Compaired the threads on the males and screwed the metal plug into the female brass. I hope this helps ? So the fitting that is in the pump is a 1/8 to 3/8 npt bushing.