As a general rule, disconnecting the battery is all that is needed. The ground should be placed as close to the area being welded as possible. The idea is that you don't want the current to decide to take a path throught the computer. I have had people say that they had to disconnect the computer. On some cars, that can cause some real problems. I have also heard people say that you don't have to disconnect the battery. I would just to be safe. It's easier, and cheeper than replaceing the computer.