Installing new fuse box...wiring not obvious

So I noticed I had blown a main 20A fuse on my 81 KZ550. Ordered new fuse box assembly from Z1, and it came with a spare 20A fuse. So i thought I would try to first just replace the 20A fuse. Bike started up, but I smelled a burning smell and then bike wouldn't start, and dead again. Fuse blew again.
I am now trying to install the new fuse box assembly, but the wiring it came with has a four plug connect that does not jive with what I'm looking at existing wiring (see photos). I am definitely not electrically inclined and was hoping it would be simple matter of unplug old one, plug in new one! Not so much....thanks for any advise. Of course the big question is, what's blowing the fuse to begin with.

You received incorrect fuse block, contact z1parts, describe what you have.
Electrons are flying at a rate the fuse finds unacceptable.
If you smell something hot or burning check harness for melted insulation or anything unusual.

Your KZ550 fuse box symptom of a blown 20A fuse is a known problem. The problem is likely the fuse box or worst case another electrical connector which runs through the 20A fuse. While you're waiting for a new Z1 fuse box try cleaning the 20A fuse contacts with a piece of scotch brite pad. Get the connectors back to shiny bright metal and verify the connection is tight. Dirty and loose connectors increase resistance and cause voltage drops. Cleaning the fuse connectors may reduce the resistance across the fuse to the point where you're not blowing the 20A fuse.

The KZ550/GPz550 fuse box is a nominal design. Dirty electrical connections, loose and corroded grounds and increased resistance all contribute to increased load which can result in a blown fuse.

So when it fried the 20A fuse, it welded the metal fuse head to the terminal. Now i guess I have to replace the entire fuse box. the wiring colors of the new fuse box are the same as the original, it just has a four pin terminal connector where the old connection is a wired pinned connection. Can I just cut the wires at the existing connection and splice it to the new four pin box? The photos I attached may help? Thanks

Yes, as you said, the big question is whats causing the fuse to blow in the first place.

You need to carefully inspect all the wiring especially the connections. Lots of connectors under the seat and behind the headlight.

I had similar problem once. I removed the tank and checked everything to the headlight shell. Opened the headlight shell and found a connection which was held together with hockey tape (PO) had come apart and live wire was touching inside of headlight shell.

You'll know it when you see it especially if you smell burning.