oil pressure sending unit

Is is just in front and slightly above the oil filter. There is (probably) a rubber cap on it and wire running from beneath it. If you slide the rubber cover back enough to disconnect the wire, then you can remove the unit by spinning it out. It can be loosened using an open-end wrench on a fitting near the base.

Luther

Do I have to drain the oil?

This unit is mounted on the output side of your oil pump. I have not changed one on an engine with oil in it. I would guess that some oil will leak out, possibly emptying the oil filter (worst case) - possibly not. Certainly don't need to drain the pan.

Luther

One suggestion, from someone with first hand experience: use some sort of penetrating lube or something like that to get in there and get that thing loose. i did not and as of right now, i have a broken off oil pressure sending unit threaded into the side of my block with an easy-out removal tool broken off inside the bolt part of the op sending unit. long story short, i have no clue how to get it out. think along the lines of screwing a bolt into the side of your block, then cutting off the end so you have no way of getting it out.