Many times the problem with the tach is bad connections. I believe your tach harness pulls straight off and is not held on by bolts. Just clean the posts on the tach with a wire brush and put some dielectric grease on them when clean.
Smart Tabs are definitely a good idea.
Boat looks very nice, congratulations!
2006 Bayliner BR205
A1 Gen 2 1.47
5.0 carb engine