1996 Sea Ray with Twin Mercruiser 7.4 carbureted engines. Both engines ran fan 2 weeks ago, went yesterday to pull the boat out and port motor would not fire, and had the oil pressure warning light illuminated on the dash. Found that the carb has fuel, but we had no spark. Cap and rotor were corroded so we replaced that, and also swapped a known good coil in. Still no spark. I then Disconnected the oil pressure switch (by the oil filter) and the warning light turned off, and the motor would now try to fire like every forth revolution, but still not able to start. Is is possible that the oil pressure switch is cutting spark? The warning light would illuminate before the engine even started cranking.

Nothing wrong with seeing the oil light with the motor not starting, this isn't the problem for no spark

Carb motors run thru the TBV troubleshooting guide

Oil light is on because the key is in the on position and there is not enough oil pressure while just cranking.
I highly doubt it is causing your issue.

you changed the cap, Id re check your plug wires for correct firing order

Forgot about this chart, thanks for sharing. The only thing I haven't done on the is check for 12 volts at the red/white stripe wire, and the ground test with the green/white wire. The fixes after those are, ignition module, coil, and pick up sensor. I have put a known working coil on so it looks like I'm looking at a module or pick up sensor

oil light comes on before engine starts cranking, and does not go away when cranking. The oil light for the other engine does not come on at all through the starting process.

I did verify this

Needs a bulb or a bad connection

Ryanw10 check the wires coming from the pick-up and connecting to module inside dist. I had one corrode away,lose connection, and no spark.

Where is this oil light that your are referring to???