oil guages are notoriously unreliable.
The red light flickering, on the other hand, is something you must attend to. One thing is good, the red light is working! The red light is supposed to come on with the ignition, then go off immediately the car is started.....and stay off (it goes off at ca. 5 psi)
Check the wiring to the sender is not loose (single wire), or the connection is not corroded or wire chaffed and earthing out somewhere as the engine is shaking - if it earths out it will turn on the red light. (on my 1990 spider, this sender is screwed into the left side of the engine block, just behind the alternator)
You can pull the wire from the sender and earth it and you will see the red light goes on.
My 2.0 spider (hot engine) runs on the motorway at ca. 60 psi and ticks over (hot engine) about 14 psi......but that is again reading the guage....actual readings might be slightly off.
If you really want to find out the correct oil pressure, take out the "low oil pressure warning light sender" or the "oil pressure guage sender" itself (whichever is easiest to get at, usually the oil pressure warning light sender) and screw in an oil pressure tester in its place (tester guage looks like a cylinder compression tester) - then you will know for sure.