I had a similar problem on my Ford 1900 a while back. I did get a new sensor and it still did it. (lightly flashing around idle speeds) I then bought a oil pressure gauge and duct taped it to the hood. Pressure was fine. And I put a T in the line down there with some iron fittings and magically everything worked ok. No more flashing. Personally I think some "gunk" got stuck in there from the 40 years of use and when I cleared out the junk and had a gauge it then showed fine. It was a weird thing how that one went too. I've since sold that tractor a few years after doing that mod. The Gorilla tape I used to hold the guage to the hood had to be replaced once but otherwise that gauge worked fine on there with the plastic line that ran down to the T I put in. No more "flashy" oil light.