Welding Tips and Tricks

I recently had my aluminum boat welded by a great guy in town. Since that welding my outboard has stopped working electrically, I talked to a friend that is a proffessional high freq aluminum welder and he said the welder grounded via my out board electronics, has anybody seen this happen and what should the welder done to prevent this?

The rule of thumb is to unplug the ignition box and keep the ground as close to the work as possible.