oil pressure switch

I have a 1993 gmc jimmy a few days ago it started leaking oil the oil pressure gauge started going up and down and now the check gauge light is on. Now I was told to change the oil pressure switch I got it off and now I can't put it back on. I didn't see or hear anything break I have the right one it looks just like the old one. I even tried to put the old one back on and now it won't go back on could some one please tell me something I can do or what I am doing wrong. I am loosing my mind.:banghead: :confused: :screwy:

It has NPT (right hand) threads and requires a special socket to tighten it. Other than that there is nothing special about it, it just screws in. The distributor is an obstacle, but does not need to be removed. Teflon thread tape is a good idea but not manadatory. Was the old sending unit leaking oil?