You replaced the temp sensor. The oil sensor goes directly below the oil filter as 4crawler stated. If you look at the motor mount next to it you will see a plug like the one your talking about. I doubt you need the plug you just need an oil sending unit. make sure you get the correct one or you gauge will fry.

85 SR5 4runner....Too many hours of work put into it, Hacked, Beaten, and Still running after all I've put it through

87 Turbo Pickup...Bought Her for $500 put another $500 in her and she's running like a dream.