Help me identify this battery draining 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!

 

[drewpy]

looks like its a live feed to the rectifier.

If its connected to the battery, its wrong as the rectifier will be live too and drain the battery.
This Should be on a switched live.

 

[vim420]

What exactly do you mean "on a switched live." Not exactly sure what to do and would like to deal with it asap as the wire is live.

 

[drewpy]

a switched live is a wire which becomes live when you switch on the ignition switch.

I see the PO had bypassed (looks like it) the other red wire.

best way to find out is to start the bike without that wire connected to the battery and see if it is producing any volts at the battery.