I have a 96 200 hp efi 2.5 liter mercury. I have owned this boat for several years with out this problem, although recently I am getting a beeping alarm when I am running in rough water. The motor is running fine and gives me no alarm until I hit rough water or a boat wake at high speed. The alarm immediately goes off when I let off the gas. Any suggestions on what it may be?

Which alarm is it, solid or interment? One for o/temp - solid noise, interment beeping for oil or water in fuel filter.

its the oil alarm in your reservoir under the cowling. make sure its full and purge if necessary.

Check all of the lines going to the main oil tank for kinks or something on top off them. Then make shure the oil pickup screen is clean on the side the lines attach. Then make shure the caps are sealing good on the main oil tank. Start motor and check with soapy water.

Would the oil issues only show up in rough water? I can run all over the lake and it only starts beeping usually when I run through someones boat wake at a high speed.

Thats what it sounds like if its an intermitant beeping. Tha tank on tha motor is tha only one that gets josseled around and has an alarm on it. Might wanna check tha float contact. Tha "in boat tank" has no alarm on it and tha rotation alarm wouldn't make a difference on rough or unstable water. Tha tank on tha motor "should" stay full under any conditions as long as tha main tank has plenty of oil. If not ya might need ta check tha valve fitting (below tha starter) feeding pressure to tha main (in boat) tank and/or tha tank and pick up itself.......jmo

Ok thanks for the advise I will make sure and take a good look at the oil tank on the motor and go over all the lines.

I forgot about tha "water" thingy. Its a contact thats at tha bottom of tha fuel filter. Tha little box with a red led is on tha bottom of tha plenum that "should" light up if water is present. Gives tha same type alarm as an oil problem. Pull tha filter and check for water. Could be tha culprit but kinda doubt it...........

If all else fails clean the fitting at top of motor mounted tank where the oil enters. Have seen a couple stop-up their.

I have the same motor however mine is not an EFI. I had the same problem with the alarm sounding mainly in rough water. The sensor in the oil cap on the reservoir under the cowling was broken. The oil cap was changed and seemed to have corrected the problem. The alarm has sounded in rough water only one time since the repair. I may need to check some of the other things that have been suggested.

Most of the time when I run into this it's the fuel water separator there is a switch screwed into the bottom of it and when water hits it it sounds the alarm

This fixed same problem on my 98 200 EFI. The oil cap sensor is basically a cork that floats up/on a shaft. They begin to stick over time. Running in rough water compounds the sticking issue.