The annual ritual of getting the Christmas lights to work! You might even feel that you would need to take an electrical training course to just get them all working properly ! And to stay on for Christmas Day! Luckily, you don't have to go to all the trouble of taking City & Guilds NVQ with Part P on this occasion, but it is one of the rare instances! Regulations are very strictly defined as to what you can and cannot do with electrics around the home, especially when it comes to house rewiring and installation. Short weekend courses are always available for all those who would like to take their knowledge further.So what to do when the lights suddenly go out?Check the Individual Light Bulbs : You should have already done this at the very start. Often the cause of the problem may simply be that one or more bulbs are loose in their sockets, a bulb could have fallen out completely or a bulb wire bent to the side so it isn't making contact. Usually, you should have some replacement bulbs that came with the lights if recently purchased. More likely, this won't be the case - so you really do need to check earlier and don't leave till a problem occurs and you won't be able to purchase replacement bulbs or new lights.Check the Fuses in the Christmas Lights : It may be as simple as a fuse blowing within the light set itself. Located within the plug should be a couple of fuses. They are hidden behind a sliding door that is clearly marked. Simply unplug the lights and slide the cover to expose the fuses. Remove the fuses and check them with an ohm meter. If there is no resistance, they are good, but if there is infinite resistance, they are faulty and should be replaced.Check the Circuit Breaker or Fuse Feeding the Circuit: Go to the fuse box /electrical panel and check to see if any circuit breakers are tripped or fuses blown. Use a circuit tester to see if the outlet that the lights are plugged into is hot. If not and the circuit is on, turn the circuit off, remove the outlet, and check the connections to the outlet.When lights go out in domestic household, it is invariably a problem of 'loose' or lack of connection or a temporary circuit overload due to plugging in a device that draws more supply than the ring circuit is rated to supply. Incorrect 3-pin power plug wiring must always be suspected and checked - bare wires touching cause shorts, or worse! If a plug fuse has blown, it's not always obvious, so replace with identical rated and known working fuse( pre checked in another appliance or with a circuit tester).