I assume you have an MFS9.8A3, right? How old is it, and how many hours are on it? What is your oil level? What oil are you using, and when was it last changed?
The oil pressure sender is a simple "ground out to turn on the light" arrangement, and comes on around 4 psi and below. It's located near the thermostat housing, on the starboard side, near the top of the block. Normal oil pressure when warmed up and running 10w-30/40 is about 14 PSI at 950 RPM, and about 48 PSI at 5000 RPM and above, so the LED typically is only on while the system is pressurizing (right after starting) for several seconds. The actual oil pressure can be tested by unscrewing the sender and attaching an oil pressure test gauge to the motor.
If the oil is overfilled, even a drop, it can cause aeration of the oil, which can result in low oil pressure (as well as excessive crankcase pressures). Likewise, if the oil level is way too low, you can be sucking air into the oil pump occasionally, resulting in low oil pressures. If the oil has a lot of blow-by dilution (especially prevalent on low-hour motors that idle a lot in cool water), the oil will be thinner than it should be, and the pressure will be lower. Typically that is accompanied by overfilled oil. Also, if there is sludge clogging the oil pickup strainer, that can result in low oil pressures.
It's not unheard of to have an oil pressure sender that fails when hot, or fails intermittently. Used to happen on US cars a lot. Likewise, if the wire to the sender has managed to ground out somehow (routed too close to something hot or sharp), it will trigger the light. An oil pressure test will confirm the actual pressure.
I would verify oil level. If the motor is not fully broken in yet, I would consider changing the oil, especially if it the level is on the high side. Likewise, if the oil has 100 hours on it, it's time to change it. Be sure to use (NMMA-certified) FC-W rated oil. 10w-30 is fine; 10w-40 is OK if you run in very warm weather all the time. Since some old oil will remain in the motor when draining, be sure to verify the level on the dipstick when filling, since you will not need the full 800 ml, and you NEVER want to overfill.