oil pressure strangeness in 4kq

[Bob]

Having strange issues with the oil pressure light/buzzer  on my 4kq.  It
has been sitting for about 2 years, started it up with bad gas and all..
ran fine of course :)

Driving it along though, oil pressure buzzer and light come on at about
2500 rpm. Back off, it goes off. Hmmm..  2 year old oil I figure. So I
go home and change it and the filter.  Still does it.

Strange thing is, when I start it, the oil pressure light is only on for
a second or so like normal then goes out.

In my other 4000Q ive bashed in the oil pan, and you can hear the
lifters rattling away from lack of oil to them, and the buzzer never
came on. Now when the buzzer does come on, I dont hear lifters at all,
so Im not really thinking there is something wrong with pressure.

Also, driving down the hiway, at around 3000 rpm the buzzer and light
went out, so I kept driving. For about an hour at 80mph which is about
4000 rpm. No problems at all.
Im guessing wire is grounding out somewhere or the pressure sender is
out of spec.  Anyone BTDT on this? First place to look?

Thanks!
Bob