90hp Water pressure gauge

[Donald Boyer]

Mercury 90hp
1988
s/n 0b312461

Hi all,

I want to install a water pressure gauge on my boat.

Am I correct in thinking that I use the port that if near the spark plugs (currently has a brass bolt in it)?

What thread size does this port have?

And I need a 15psi gauge?

Thanks in advance,

Donald.