Help me identify this aftermarket battery lead.

[vim420]

I recently purchase a 1980 xs400 with fairly low miles and very clean body.
The battery would never hold a charge longer then a few days. Upon inspection I noticed there was two leads on the positive terminal. So I unhooked the one that I assumed was aftermarket and now my battery holds a charge and I can use the electric start after a it sitting for a week. When I reconnect the other lead it always ends up dying. When it's not connected everything works fine and there are no visible aftermarket electronics hooked up.
http://imgur.com/a/NHN8l
You can see the wire shodily crammed in with another wire.
I plan to just remove it but if anyone has some insight as to what it is that would be awesome!!

 

[xschris]

Not sure what it would be for? If the bike works/runs and is charging like it should I would just remove it.

 

[BBS360]

Looks like it's in parallel with another wire between battery and fuse connector? Does it bypass the fuse box?
Might have been someone's bright idea for an emergency connection in the case of a fuse blowing.
Remove it or tape it up with electrical tape until you can investigate further.

 

[vim420]

yes it bypass' the fuse box