Tachometer voltage rectifier

I recently replaced a voltage regulator on a 75 HP Mercury Mariner.

I understand that the 2 yellow wires that feed the rectifier can be wired to either side of the 3 post voltage rectifier.

There was also another grey wire that I was told is for the tach.
There is no tach on the boat. Should it remain disconnected? It was connected, but not sure where it runs to. There are no extra wires under the steering controls.

I seem to be charging up to about 16 volts when running 1/2 to 2/3 throttle. Is that going to damage the battery?
Should there be another voltage regulator installed between the rectifier and the 12 volt line that feeds the battery?

The battery is the regulator...must be a wet type not maintenance free

so it is designed to boil the water out of the cells?
I think there should be a better way to maintain voltage, & limit it to 14.0 volts at the upper end.
Will I damage my maintenance free battery? maybe the voltage output isn't a problem, I didn't check it at full throttle. Not sure how many amps it charges at.
Worried that it could damage other electronics fish/ depthfinder, etc.
Is it possible the rectifier is no good?

I think I figured out where the tach wire runs. It seems there is a 5 pin connector on the Quicksilver controls that would be port to install a tach.