Good luck...I have talked to Skiers Choice and Indmar, and they all start acting like I am not speaking english when I ask about a wiring diagram.

The bottom line is this...a 20 amp fuse will blow every time if it is seeing 37 amps of draw. But, there very well may be a relay between the starter and the key switch. The easiest way to check without a diagram is to disconnect the small post from the starter, turn the key and see if you hear a clicking of a relay on the boat. In a well designed system it will belocated rather close to the starter...so somewhere in the engine bay.

If there is no relay, then perhaps the 20 amp fuse was supposed to be a 40 amp all along...