That sensor sits in the oil tank and triggers the oil light on your dashboard when you're low on oil. I don't have the shop manual handy to know ohms, but there's an easy test. If you pull it out and turn on the ignition, the oil low light should turn on. If you put it back in the oil tank, the light should turn off after a few seconds.
The white area is the sensor. It has a couple holes in it, I think to allow oil to flow in/out and trigger the sensor. You can see the hole at the top in your picture.
Replace the rubber grommet if you haven't. It's the rubber part that goes into the oil tank. The grommets get old, dry out, and stop making a seal. Order 2 (one for the oil sensor at the top and one for the red elbow at the bottom of the oil tank). It'll stop any oil leaking out of the tank into your hull. Kind of a pain to get the grommet over the white area, but just be careful and lubricate it. Make sure you put the grommet in the hull FIRST, then try to insert the oil sender. If your grommet is good, you can't get the oil sender back into the oil tank if the grommet is on the sender unit. I just replaced my grommet yesterday.
The end of the sender unit is a one-way air valve. No hose goes into it. I think that's to allow air into the oil tank as the oil is used.
