I got a Mech Mod once and it was Arching to the Battery.
The cause was the throw of the Fire Button was just barely making contact with the battery when the button was Fully Depressed.
I put a Red Computer Mother Board Insulator under the Contact Pin to move the Contact Pin closer towards the Battery. And the Problem went away. It also Fired more Reliably.
Not Sure if this is what is going on with your Mod? Because the Picture you Posted is all Black for some reason. But something that you might want to Check.