Re: mariner 40hp mag alarm
Oil reservoirs have a common problem with the float. The float is a foam block with a magnet glued to the bottom. The magnet triggers low oil switch. The magnet has a tendency to break loose from the foam and sit in the bottom of the tank triggering the alarm. The jolt of the rock could have knocked the magnet loose.
A new oil tank is the only solution since the float can't be removed without cutting open the tank. You can confirm this by disconnecting the wires from the tank. The alarm should stop. Another test you can do is remove the tank and turn it upside down. the magnet will move away and the alarm should stop.