2003 bombardier 90hp. tach doesnt work

[Fishfinda tackle]

My tach wont budge. I just bought a 2003 angler center console. Everything else seems great on the boat but its reall difficult to get to my wiring...even If I did, I wouldnt know what to do. How do I find out if the problem lies with the tach itself...the wiring to the tach or the wiring on the engine end of things? I've aways had older boats / motors...so there is alot more wiring than im used to lol. My first guess is its prob. just oxidation or a crappy connection. I cant imagine the tach failing on a 2003...not yet anyway.
Any tips I could try that wont require a degree in rocket science or special tools?

Thanx everyone