My Merc keeps randomly dying. From idle to while I am plane. This may happen two or three times a trip or may not happen at all for months. I thought it was just some bad gas at first because I went almost a year and it never happened again. Now I have had it happen several times in the last week or two.
The motor always fires right back up and if I am just idling I have heard it stop for just a second and then keep running. Last info is I recently bought a new humminbird unit and while I am on plane a message flashes that input voltage is to high.

Ignition? Fuel pressure or voltage regulator?

This motor does have safety feature that will shut the ecm off if voltage gets above 16.5 volts.....OPTI

I had the same problem on my 96 efi for 2 years. It was voltage regulator. They have 2. If they are still originals, you can look at them and see which one is bad. They should be clear gell on one side and you can see circuts. They are behind your coil packs. Look and see and i will bet one looks burnt. The new replacement parts are solid black. Let me know how it goes.

or if voltage drops bolow 9.5 volts. would suspect elect. fuel pump shutting off or a loose connection on the fuel pump, battery or even a bad ecu connection

Mostly from bad battery connections. This sounds different with the high voltage alarm. Agree with changing regulators.

Awesome, I will check out my current regulators and get new voltage regulators by Friday hopefully to start with. I will post back and let ya'll know if there is a difference. Thanks for the advice.

Pulled the regulators this morning and bingo! One is melted badly and even had two of the wires melted together, luckily the same color (yellow). Never new this would probably fix my tach jumping problem also.
I ordered two new ones and overnighted them to my house. They are going on tomorrow morning. I will post in a couple days after a few test runs.

Been out twice since replacing the regulators and not a glitch since...Yippe!! Thanks

Glad to help. There are a few things to keep a eye on if you have not already addressed. The oil cap on top of the motor and small oil lines on the motor.