I spent a couple minutes reviewing oil pressure sensor switches on RA - for both the Buick 307 & the Olds 307. There ARE differences in availability of oil pressure sensor switches (e.g. 60psi vs 80 psi). I mention this because in my previous post (above) I suggested the oil pressure switch to which the OP responded he changed the oil pressure switch. However, that was BEFORE he found out he does not have an Olds 307 which begs the question which oil pressure sensor switch was installed - an oil pressure switch for an Olds 307 (most likely) or for an Olds 350?
At any rate, it might be of interest to know/validate exactly what oil pressure sensor switch was installed.

 

And that's your first mistake, right there. RA is NEVER a reliable source for part fitment info. The fact that for the 307 they show oil switches with both 1/8 NPT and 1/4-18 straight thread should be your first warning sign. No 1964-90 Olds block ever used an oil pressure sender with a straight thread. Every single one of them is 1/8 NPT.

 

Thanks for pointing out my mistake.

Your Magic 8 ball working today?

What unit did the OP install when he replaced the oil sensing switch?

 

The mind reading thing still isn't working, but the GM parts books for Oldsmobile, Buick, Pontiac, Chevy, and Cadillac show that every single 307 with idiot lights used in the mid-80s takes the same P/N 3815936 oil pressure switch, which is 1/8-27 NPT. FYI, the 1/4-18 thread sender is for the Buick V6.

 

Pretty certain I've lost my mind reading the Swiss cheese, but I think I've figured it out. The OP changed the oil sensing switch (as stated) during the period of time the OP proposed the engine was a 307. The casting number posted by the OP demonstrates a 1968-76 350 block casting number (if it was taken off the engine currently in the vehicle) & we now have confidence in the oil sensing switch employed in BOPC&C for a 307 w/ idiot lights (P/N 3815936). There's probably no difference in the oil sensing switch between a 307 vs a 350 I suppose....more Swiss cheese, please.

 

^^^This. The oil pressure switch closes when oil pressure drops below 4-7 psi. That range is due to manufacturing tolerances in the switch.

 

I’m having the same issue with my 80 supreme 260
going to try some of the suggested posts