Oil pressure drops

I have a 1986 ski nautique 2001. Last time we took it out, the oil pressure would go to zero upon acceleration from stopped. We could cruise just fine if we accelerated slowly. But pulling a skier up to speed the pressure was just staying at zero, and I ended up backing off and dropping a skier in the water because I didn't want to damage the engine. Then we started up and cruised back to the dock with gradual acceleration just fine.

I just went out and cranked it up to see and this happened. You can see it goes up to 40 psi then back to zero then up to 40 again.

https://youtu.be/Rv0y5_Y-3ic

This boat had a new oil pressure sensor a year ago because it wouldn't get oil pressure while cranking. Turns out it the previous owner had installed the wrong starter on it and the engine was turning backwards, hence no pressure. This is fixed and we've put quite a lot of hours on the engine since with no problems until this.

Other odd thing is it drops completely to zero and suddenly pops back to good pressure. There's no in between.

Any ideas? What should I check?

Thanks

+1

Thanks, I'll try troubleshooting electrical a bit more and if necessary I'll run get a mechanical gauge and try that. Appreciate the help!