I have a new mercury 9.9 outboard motor. It has about 2 hrs running time on it. The oil pressure light will illuminate and engine won't accelerate.

Question edited for a lot more clarity and correct spelling of the maker.

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The oil pressure warning light is designed to illuminate any time the oil pressure is too low (below a pre-set engineering-specification). Low oil pressure can be caused by an oil level that is too low, a faulty oil pump or worn out engine bearings. The light could also potentially illuminate if the engine idle speed is excessively low (near stalling condition) due to the slow rate of pump rotation. There is also the possibility that a failure in the oil pressure warning circuit is causing the light to illuminate inappropriately; this could be the result of a failed oil pressure sensor or other wiring issue. Because the other symptom present is an engine stall (shuts off) condition, I'd recommend inspecting for a mechanical issue first. Ensure the oil level is correct, then attempt to turn the engine over by hand using a large ratchet on the center crankshaft pulley bolt; if the engine can be rotated it was not stalled out by a seized condition (which could be caused by a lack of oil pressure). If the engine runs but idles low, I'd suggest raising the RPM to see if the light goes away and prevents the stalling-out. If everything appears OK with a raised idle then the idle control system should be inspected. On the other hand if the light remains on, a mechanical oil pressure gauge should be installed to the oil pressure test port (near the oil filter) to confirm whether or not the oil pump is producing adequate oil pressure. You can read more here: https://www.yourmechanic.com/article/how-do-you-know-if-the-oil-pressure-gauge-is-bad

Too much oil in a four-stroke engine can cause too much pressure in the crankcase and force oil out of the crankcase breather or past the seals that normally keep the oil inside the motor. This can leave oil outside the engine which then slowly continues to wash off into the water.
Clean the outside of the motor (inside the external casing) with rags and/or degreaser and lots of water to remove residual spilled oil.
Recheck oil level again after running the motor.
If the over-pressure was very high it's possible that a seal is damaged and will continue to leak after the oil level is corrected. If this is the case you might be able to see freshly leaked oil somewhere (after running the motor) to find what needs fixing (e.g. a new gasket or seal may be needed).

the serial number begins 2487558 and continues past 2491265 and as the beginning serial number denotes the year , your engine is 1969 model
it shows as a 2 stroke with auto oil injection
check the heads
if the plugs are in the flat of the head and there are no rocker covers it is 2 stroke
talk with a mercury /mariner service center

The low oil pressure warning lamp will illuminate anytime the ignition switch is turned to the ON position without the engine running. When the engine is running, the light also illuminates if the engine oil pressure drops below a safe oil pressure level. To test the system, perform the following:
If the oil pressure light does not work, perform the following:

1. Turn the ignition switch to the ON position.
2. If the lamp does not light, check for a broken or disconnected wire around the engine and oil pressure sending unit switch.
3. If the wire at the connector checks out OK, pull the connector loose from the switch and, with a jumper wire, ground the connector to the engine.
4. With the ignition switch turned to the ON position, check the warning lamp. If the lamp lights, make sure the oil pressure switch is properly grounded in the cylinder block, and if so replace the oil pressure switch. If the lamp still fails to light, check for a burned out lamp or disconnected socket in the instrument cluster.

To diagnose an oil pressure light that stays on, perform the following:

1. Check the engine oil level and top off as necessary. If the engine was 2 or more quarts low on oil, test start the engine after topping off the oil level and recheck the oil pressure light operation. If the light stays on, stop the engine immediately and go to the next step.
2. Disconnect the wire at the sending unit, then turn the ignition switch to theON position. If the light remains on, check the wire from the sending unit to the gauge for being shorted to ground and repair as necessary. If the light goes out, turn the ignition switch OFF and go to the next step.
3. Replace the oil pressure sending switch with a known good switch.
4. Start the engine and check the oil pressure light operation. If the light stays on with the engine running, stop the engine immediately to avoid severe engine damage until the cause of the problem can be determined.

WARNING
If the oil pressure light remains on while the engine is started, stop the engine immediately. Do not operate the engine until the cause of the problem can be determined. Operating an engine with low oil pressure will cause severe internal damage.

Possible causes for an oil pressure light to stay on are:


Pinched or grounded sensor wireDefective oil pressure sending unitRestricted or severely leaking oil filterExcessive internal engine bearing clearance.Insufficient or severely contaminated engine oilBlocked oil pump pickup screen or severely worn oil pump

Back during the time these were made, you would be advised to use a 30 HD.
This oil would be appropriate for all use except real cold weather, when a 20W-20 would be better. ( below 40 degrees farenheit)
(Do not use a non-detergent.)
A few years later, the recommendation changed to 10W-30.

where do you see the oil?

Water gets in your engine through the exhaust with the boat speed! Lift that engine when not in use!

2 cycle, 50:1

Dont have the manual in front of me...recollect that there's two types of warnings. The pulsating warning is oil (starts with 30 minutes of oil left) or the fuel filter (or sperator, something like that) may have water in it. Running outboard with cover off, is a little black box that would have a red light lit if that's the case. If oil full & no red light, may be oil injection system...would also check to make sure lines aren't pinched, etc. Mine has been specific to oil the two times its gone off.

The full non-pulsating is engine overheat. Not sure beyond that.

Not much, but hopefully gets you going.