On a competition box the closest pins should give a hit indication. These can be tested as for the bodywire. In dire emergencies a ground lead can be replaced by a body wire leaving the box off set. Plugging your bodywire into the other spool can determine if the spool or the sword is at fault. If the ground leads are exchanged then the fencers effectivly switch ends hopefuly resolving doubt about where the problem lies.
Common sense is the best asset for an armourer.
Many problems have been solved by taking a step back and applying a little common sense.