School bus welding must be performed with the batteries disconnected or a surge protection device attached. Today's school bus or any vehicle for that matter have many electronic features that are very sensitive to voltage spikes and surges.
I worked on a school bus today that needed welding around the battery box so instead of having to disconnect everything, I used a surge protector we picked up from 'NAPA'. It's a simple looking device that has to be hooked up to the positive and negative battery posts, when it's working properly a green LED light comes on.
This prevents having to re-program everything on the school bus and fooling around with cables and wires, the part # is 95257 .
This is an important step to take when welding on a school bus.