No apology needed, I didn't dismiss the pressure switch issue, I just thought I actually HAD tested it.
Which is why I moved on to DTCs as a possible cause of the alarm.

Like I said, I appreciate any help, this boat was so beat you'd think they did it on purpose. I didn't know nearly enough when I bought it... and some days regret buying it!

Off Topic:
Things I've had to fix because the previous owner was brain dead.
Engine Alarms
Shifters
Trim Tab wiring
Trim Tab Motor
Radio (was none)
anchor locker
Bilge Pumps
Blower motors (neither worked!)
bow light (didn't work)
distributor cap, plugs, wires
trim rams on BOTH drives
flame arrestors soaked with oil
glove box broken
Horn button AND noise maker broken
stern light base broken
trailer brake pads gone
trailer tires shot - 2 wouldn't hold air

So.. yea... feeling a little ripped off and stupid here. Next time before spending $ on a boat, I get a full inspection!

I also had to do the JR Marine transom fix to both over the winter.

Hey BUP his serial number may be in the range of the fuel pressure sensor area, don't know for sure but figured you would. That said he won't know without a scan tool and seeing if he has

MCM 5.7L EFI: With D7ED or D798 checksum.

STS, the oil sender is below the distributor on the rear deck of the block, port side

Thanks, I will come back and check out if you can post engine serial number. I will admit my post was not clear at all and pointed in one direction only inwhich was my fault totally. The only thing I was clear on was the word possible.

Its
STRB Serial: 0M047350

fuel pressure sensor and IAT was in 1999 model year and fuel pressure too low cause a solid horn / beep for 5 seconds then goes off and of course had it serial number break as to exactly when.

there is a service bulletin all about it as well.

Found the oil pressure switch, thanks. That was the issue. Soon as I saw it had oil on top of it, I knew that was most likely the issue. Disconnected the wire, tested it engine off/on, and yep that's it. New one ordered.

So, of course a 16 yr old kid takes out my mailbox last night... have to call the post office and make sure I can get this part I need by this weekend!

Yes I could just run the old one, with the wire disconnected, but I already pulled the thing out.
Who could have anticipated my mailbox getting run over?!

Thanks everyone, alarm is quiet, and I fixed both DTCs I had, should be a good summer now!

Bummer on the mail box, folks around here will sit it on top a trash can or drum while fixing it.

They have the same switch at the local auto parts store, there not marine unique

POST # 3 ------- and keep in mind I never seen the switch --------------- Need Help - Merc. 350 Alarm on when engine on..

Man sometimes you guess right and sometimes you get lucky and SOMETIMES your just plain old good at what you do. Pick one.