Festive Light

[NivagSwerdna]

OK... so it's the time of year that you get the lights out of the loft/garage etc and find that less are working this year than were last year... and the way they are arranged they seem to break such that not just a single light goes out but a whole section dies.  Many of these sets now have small lights which are not replaceable (i.e. no sockets).

Last year I resurrected a favorite set by painstakingly using a multimeter and a pair of fine sewing needles to try and find the breaks... it was a slow and painful process.

Being based in blighty the main voltage in 240v so these light run through wall warts with the typical light string being 24v.

I was wondering...   Any tips for diagnosing these?

Would it be possible to wrap a wire around the cable and induce a signal in the cable and then with a probe go up the wire and sense for signal?

Some of my sets have a controller box (imagine small green plastic rectangle with dodgy switch) that controls combinations in the lighting set... I think these sets have five wires going to the lights themselves.  Any pointers for how these are wired?

Thanks in advance (and Happy Christmas),
Nivag

PS
Oh... and many of the lights are now LED.  Does that affect the tracing?  Forward Voltages?