Oil pressure Sending unit questions

Hi- This is my first post here!
:SNSign:

I just picked up an 89 5.0 GT ragtop with 82k miles on it.

After the car is warm, the Oil Pressure is running low- down around the Second mark when cruising, and the first mark when idling (bottom white mark, not the bottom red mark)

I did a search and read through a lot of posts here and it sounds like the sending units going bad are a pretty common thing... and that sounds good because an engine with 82k miles should NOT have low O/P....

My question is- in some of the posts, I read that the sending unit is basically just an On/Off switch, and even though there is a guage- it does not acutally fluctuate with RPM...

Mine DOES fluctuate with RPM right now- it acts just like all the O/P Guages I have ever seen- reads higher when cold- and goes up and down with RPM, and reads a little lower when idling warm.

Do the replacement senders NOT fluctuate?
I dont' just want to stick in an "On/Off" sender that will reads good right up until it drops below 5lbs (like an idiot light does)

anyone have any details on this?

BTW: Just changed the oil and still ahve the same results.
its running fresh 10w30 & A Napa Gold filter

Thanks-
Ben

So... I guess i fixed it-
After reading a bunch of posts about it- i went out- pulled the wire off the sending unit- tapped it a coupld times with a wrench- put the wire back on...

No more low oil readings... now it reads good- Just dips a hair below the mid mark now when idling at temp.

So I guess the sending units really are pretty flaky.
Oh well- I think that low O/P reading was the reason I got a good deal on the car- so I can't complain too much!

Thanks!
Ben