From my experience (yes I've had it too) it's not actually the plug into the light switch, it's the switch itself. Carefully prise the rear section of the switch apart, you will find a small circut board with wires coming out of it that join to the rear section bit that you just prised out. The solder around these wires cracks and causes the problem. Re-solder the wires, board and anything else that you can see with a soldered joint, snap the switch back together again and you will have no further dramas. The reason why most people find that the lights work again after removing and reconnecting the plug is that it slightly disturbs these broken soldered joints causing them to reconnect and work again. Hope this solves the problem.
Cheers
Mark
