Make sure the caps on all the oil tanks are tight. Check to make sure that the on-board oil tank is full of oil. If it isn't fill it up with oil and try running your engine again. If you have a pair of muffs you can put on your lower unit so you can run it just hooked up to a hose makes the job a lot easier. There are usually two wires coming out of the oil tank. If the on-board tank is full and you are getting the beep, try disconnecting the wires. If it is an oil alarm from here it should stop. Mercury engines have been known to send a signal from the sensor inside the tank even if the tank is full. In a lot of instances you can replace just the sensor but in a lot of cases you have to replace the on-board oil tank. A lot of the fuel injected Merc's have a sequence of 4 beeps followed by a 2 minute silence and then another 4 beeps. Before you disconnect any alarm I would highly recommend you know for sure what is causing the problem. It has been a while since I worked on any engines but I will help you in any way I can.