Blown fuse

[SAT]

I have twin Crusader 6.0’s in my 2005 Four Winns. Yesterday while running at 3400 RPMs, the port engine suddenly quit. Drove back to dock on one engine and found a 20 amp fuse blown. The fuse is in the three-fuse fuse block, right on the engine. I can’t find anything that tells me what the fuse is for. Exhaustive searches of the manuals, both on line and the printed one that came with the boat tell me only the three fuses are fuel related, but not specific like “fuel pump.”
I replaced the fuse and it promptly blew again when the engine was crancked. I suspect the primary fuel pump but it would be nice to know for sure before i drop that kind of dough. Any ideas.

 

[SAT]

Well i resolved my problem, for 53 cents. I started out by disconnecting each fuel pump in turn and still the fuse popped with the turn of the key. I presumed it was not pumps. Several days ago i swapped out the heat exchanger. Since the wires for the fuse box go behind the heat exchanger i decided to loosen the tube up and see if something was pinching. As i moved the tube to one side, out came a dangling green (ground) wire. Looking it over I could tell it was attached to something, and fortuntely all i had to do was look at the brother engine to see that a green wire was attach to the underside of the heat exchanger tube. After the purchase of a nut and lockwasher the wire was re-atch. The engine started and runs fine. But i still do not know what each fuse is for!