Dear God, a low switched mech. It seems unlikely the mod itself has a short, there's not a lot to it. If it does, it has to be in the insulator between the positive contact and the negative one, or the plate where the battery battery positive poles contact might have swung out of alignment and is contacting the back of the box. It is far more likely your short is in the topper itself, or caused by a bridge screwing it in the 510 connector. It is also possible you put one of the batteries in upside down.