Oil Light comes on at idle
 

Hi, I have a Saab wagon, 6 cyl., 2000 9-5, 100 K miles. Oil light (and audio dinger) comes on at idle and when in gear , coasting, with nogas given.
How can Iget reasonably comfortable, without an oil pressure guage, that I have enough oil pressure (take oil filler cap off while running, etc...if so, do I feel pressure at that opening ?). Don't want to drive too far to mechanic til I know pressure is ok (supposedly is if light is not on, but who knows?)
Any other suggestions as to what is causing this?I have checked the wire connection at oil sensor and it is ok.
oh yeh, oil level is fine and oil is not too thin (about 2 months old). Thanks a lot Steve