Like an idiot, I accidentally reversed the polarity when I was putting a battery in my boat. I think I may have blown that 90amp fuse. (according to what I read). I have a Mercruiser 350 EFI... does anyone know where this mysterious 90amp fuse located? I can't find it.

On the starter. It's a white block on the battery wire.

Ok, thanks. I still can't find it. Does anyone have a picture? Where is the starter located? Near the alternator?

#8 in this picture is the thingamajig you're looking for

the starter is at the r/h side rear of the engine

http://www.mercruiserparts.com/Show_...ER+%28MANDO%29

2010 350 mag efi. The fuse still on the starter? I'm working on a Southbay tri toon an there's no room to work on it. Any help would be apricated thanks

Yes the 90 amp fuse is still on the starter. Item number 8, http://www.mercruiserparts.com/bam/s...31754/15322/10

Check for 12v power at the orange power wire on the backside of the Alternator. If no power there, then there's a good chance the fuse is blown if everything else is in normal working order.
This image should help give you a better idea of the starter fuse,

Thanks lakematdude. Picture helps a lot. Have a great day.

Looks like I blew the fuse. How do I get at the starter motor 90 amp fuse. Starter motor is on bottom of engine, facing aft, starboard side and buried underneath fuel intake hose and starboard side plywood support.

Ayuh,..... This thread is 8 years old,......

Ya remove whatever's in yer way of gettin' to whatever yer tryin' to fix,......

Just like any other boat,........ or car,.......... or truck,.......... or anything else,.........

And that is a 90 amp fuse on its way out and if its an efi engine what a way to knock out the ecm. Just reporting what I see very clearly.