Wiring problem on GZ125 2003

[theironsoldie...]

I have a GZ125, 2003 and here is the problem I am having:

I started it up, everything working perfectly, and drove 5 miles. 8 hours later I tried to start it and nothing happened when I pressed the starter.

I checked all the switches, but no obvious problems. I checked the Starter Solenoid, and found the fuse was blown but was the wrong size (30A instead of 20A). I changed the fuse, no fix. I replaced the Solenoid itself, no fix.

I then manually connected the Solenoid contacts and it started up. Everything was working fine, including all electrical components. I drove it home, 5 miles, and found that the battery had exhausted(down to about 6v) to the point that it would not start again.

I am at a total loss as to what would cause these problems.

There are no obvious/visible faults with any of the wiring.

I can get used parts rather easily and affordably, but I am not sure what I need to replace. Any suggestions as to what would cause this?