Oil pressure light when idle?

Ok you guys gotta know what this means. 66 dart, 225ci, 270.
had the engine rebuilt 8 months ago.

probably have put about 500 miles on it since then.

So this red oil light at the left of the dash (stock) normally is lit when I start the engine, then it goes off and stays off.

Yesterday, warm day, I am driving around town and the oil light lit up any time I stopped accelerating, and at idle. But if I step on the pedal the light immediately goes off, I get off the pedal, light immediately goes on?

Then today, I check oil, full. and clean. I replaced the oil about 4 weeks ago.
I start it up, light stays on until I rev a little, then off, then idle back on, then rev off. So I press pedal down and rev for about 10 seconds. Now the light stays off when I let off the pedal? I drove it around town and the light stayed off???

What could possible be going on here?

thanks for any help.

I did think about possible loose connection at the pressure plug, but it seems to be on.