You pulled that wire off the copper plate, didn't you? I sure did. Twice. If you have a soldering iron it's easy to strip the wire back, reheat the solder, and attach the wire to it. Even with no experience it's an easy job.

If you don't have a soldering iron this might be a problem. It's not entirely necessary for the flash to work (I put it back together and fired off a couple shots without it) but I wouldn't recommend it. Nikon calls it the insulating plate but I'm not sure what it's for.

The repair manual says not to use anything other than lead-free solder and to use a tip dedicated to lead-free solder on your iron, but I'm not sure how important that is.