The main fuse is supposed to be 15A.
Common occurrence is for the fuse contacts to form a resistive oxidation layer that heat when current is passed through it. The fuse should normally run at about 2/3 of it's rating which provides some, but not all, of the heat needed for it to blow. if you add the heat generated by the fuse clip oxidation resistance, the fuse usually melts at or very near the end cap.
For those that don't know about this situation, they put in larger and larger rated fuses that can withstand some extra heat. The fuse holder plastic then starts to melt and the fuse clips lose their temper or spring clamp pressure, making the heating issue ever worse and more problematic.
If your fuse holder is in otherwise good condition, you can polish the contact area bright and shiny, to solve the problem for another 15 years or so. However, if the holder has gotten bad, a replacement is needed.
You should also test for fuse retention pressure. There should be enough pressure that you need a tool to remove the fuse from the clips. If you can pluck it out with bare fingers, the clips have lost their tension.
It is also important to use the correct length fuse, so that the clips have maximum contact area with the fuse ends. I think the 76 K model still uses the 1 inch length fuse. But, I don't have one of those.
With stock lighting, coils and other electrical equipment, the stock 15A fuse will run warm to the touch. If you can't hold your thumb on it while the bike is on, you have issues with the fuse holder.
You can search here for "download manuals" and find the shop manual for your bike, including wire diagrams.
Rather a pity about yet another cafe conversion. There seem to be so few that appreciate the bike for its own greatness as it is. But, it's your bike. If your acquaintances don't appreciate vintage gear, you'll likely only get admiration from them with flat black paint, pods, clubmans, knee dents, invisible blinkers, and a rear fender/seat that put road water and grime on your back.
Cheers,
