2017 Mahindra XTV 750 Mpact Electrical Issue

[Ernie Beast]

Pulled the battery to put on maintainer over the winter. 4 cable wires, 2 on right frame rail, 2 on left frame rail. I zip tied positive, zip tied negative to keep from confusing when I reconnected. Installed negative cables to battery first. When I started to tighten cables, something arced and put a weld mark on the bolt. What could have back fed current to the negative terminal? The battery was out of the unit for approximately 2 months. I cannot figure out why this happened? I need help please.

 

[kneedeep]

Did you touch something with the wrench?

 

[RjCorazza]

Pulled the battery to put on maintainer over the winter. 4 cable wires, 2 on right frame rail, 2 on left frame rail. I zip tied positive, zip tied negative to keep from confusing when I reconnected. Installed negative cables to battery first. When I started to tighten cables, something arced and put a weld mark on the bolt. What could have back fed current to the negative terminal? The battery was out of the unit for approximately 2 months. I cannot figure out why this happened? I need help please.

I am not totally clear on what was connected, and when... However, the mistake that is generally made is that people connect the negative cable, then the positive and accidently short to any bare metal.
When removing a battery always remove the negative cable first. When installing the battery always connect the positive first. In any scenario a tool across the terminals is a dead short and can be bad news.