No the B+ powers everything in the back eg lights, amp, seats I think, windows maybe. If you blow that fusible link a whole bunch of stuff stops working. I can't imagine any amp is that demanding, but putting a 60A fuse there won't do anything because the fusible link will blow first... I'd put a smaller fuse and see what it does... worst thing you blow a fuse.
Connector is like WC says, it's just a junction post.... no fuse in mine though.