Mine snapped right where the wires go into the plug. Had to go to the scrappies and cut the plug of another golf (think it was for the brake pad warning or similar as most had the engines already out) and cut, solder and shrink wrap a new plug and short piece of wire to the existing loom.
Wiring on the mk4 is similar to a peugeot 205 in places. Not related to the reverse lights but worth checking the wires which run through the rubber connector from car to tailgate too. Mine snapped here and I lost the rear screen heater, also melted into the washer hose.. worth a look just as routine inspection.
Sam
