7.4MPI does not turn over
 

I am trouble shooting a 260 powerquest (7.4 MPI) that won’t turn over.

Volt meter is reading 12.6V from positive wire on starter to ground on battery, turn the key, starter solenoid clicks, volts go down to 12V then nothing. Starter squealing very slightly but engine does not move. Checked everywhere for voltage drops (ground on block and other areas) and nothing shows a drop.

Last time we took the boat out:
Engine was running fine as usual, but we notice the volt Gauge was reading a little below twelve and did not move with RPM change. Usually it will go to 13ish at 3500 RPM. Brought the boat back to the lift. Turned it off. Tried to start again and would not turn over anymore. Batteries have been tested positive.

thoughts?