Its a good while since I've repaired one of these, but I recall the wire being riveted up via one of the tubular rivets on the back of the brass contact plate. Its possible to solder it back on, but is tricky due to the low melting point of the plastic. I would remove the remains of the crimp from the detached wire and make sure the strands are clean and unoxidized. I use a glass-fibre pencil to remove any surface corrosion. Tin the wire with tin/lead solder (unleaded requires a higher melting point). I like to add a little rosin flux gel used for electronics work to improve the flow. Now, here's the tricky bit - fold up a piece of abrasive paper and clean the underside of the brass contact plate on the right hand side. Once done, apply some flux underneath. Using a fine tipped, hot soldering iron angled to get just under the edge of the plate, heat it just enough to get it tinned underneath and on the edge. Hot and quick is the technique. I instantly cool the area with freeze spray. You need to beat the thermal creep that will soften the plastic. Apply some more flux to the wire and get it positioned under the plate ready to solder - I use Blu Tack to leave both hands free. You want a little bit of wire exposed. Heat the wire and feed in some solder on the junction. Work quickly and cool down the area immediately afterwards.
The wire breaks because of ineffective strain relief. Once soldered up and the wires secured, a good repair will last indefinitely. My Wife's old V50III still has the repair I did back in 1990.
