Wiring question Neo Cross

Upland Mike

New Member
I have a few wiring questions.
This is the back of the connector the battery connects to. Small black wires go up to the computer. Large red and black go to power plug. Yellow wire goes to power plug (see second photo). Then on to the controller. What is the purpose of the yellow wire that starts at the battery connection and goes to and through the white battery plug?
I'm building my own battery to hook up to the bike. (36 volt 13 Ahr) I don't have an original battery so I need to bypass the original connections.
Thank you for your time and expertise. Any help would be greatly appreciated.
Thanks,
Mike