The single cable lights which we use on our christmas tree failed one morning and i have not been able to find the fault, despite doing the usual checks of cable connections to and fuse in the plug and checking each bulb. They are not connected to a transformer but do have 2 white tipped fuse lights in the string. Is there a simple way of fault finding I can use?

Fred Little, January 2010

You need a multimeter set on continuity,when testing each bulb you will hear a buzz to say its ok

ajleech, January 2010

I would agree with Adam. If the lights are troublesome then you are better off replacing them unless they are of sentimental value to you. The newer LED lights are not without their problems either. They will have a transformer ( which can go belly up ) and they tend to be non replacable bulbs.So you might end up with a string of lights with some working and some not and not be able to fix them.

Gary, January 2010

The dreaded christmas tree lights !!
I presume that the string of lights is wired in series ie: when one bulb goes they all go.

I assume that the plug top fuse is not blown and the wiring itself is not damaged. If this is the case then it has to be one or more of the bulbs.

You say that you have checked all of the bulbs but trust me as an electrician it is very easy to miss one as I myself have done. There is a little device that I find invaluable that you insert each bulb into and the bulb will light if its good.For me it is the only 100% way of being sure that all of the bulbs are good.There are so many lights on these strings that its easy to miss one. These are available at DIY shops. Regarding the white tip bulbs , these as you say are fuses that double up as a light. Do not replace these with a regular bulb. Happy Hunting

Gary, January 2010

The old style Christmas tree lights with a twisted cable and all the lamps in series are notoriously frustrating to find faults with, but are very simply constructed.

Apart from checking the plug (fuse, connections, pins), cable and all the bulbs, there's not much else you can try.

This type of lights is known in the business as a class 01 appliance because it is neither earthed nor has double or reinforced insulation, and isn't recommended for sale or use in the UK any more, so you could use that as an excuse to get a new set of LED lights for next year.

Adam, January 2010