Christmas Tree stop/tail lights.

[Riejufixing]

Multi-LED stop/tail lights as fitted to many 125s.

Some of the LEDs function sometimes, leading to odd and variable patterns of light bulbs.

Three wires (black, blue, yelow) go from a plug on the wiring loom, in a PVC sheath, and change in there to black, red and yellow before being soldered to 5 circuit boards. I don't know what happens in the join, but the circuit boards and connections are pictured.

Any ideas about what may be wrong? I was expecting to see some sort of spring contacts, but no, they're all soldered. Fixable?

EDIT: Dry joint seems possible? Looking at second board in from the left in particular.

[Easy-X]

Dry solder joints sounds about right if it's intermittent. Unscrew the boards and jiggle each LED, see what happens.
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Royal Enfield Continental GT 535, Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[WD Forte]

I reckon its case of buy cheap buy twice
For starters they're wired in series which isn't best practise
because any variations in one LEDs electrical characteristics will affect others on the circuit.
Also if one fails open circuit they all go out and
if one fails short, the others get overloaded.

I did similar quick bodge on a non essential boot light and got similar results.
where some started to break down.

A few years back I did some experimendal bodgineering on me old thing and wired all the tail light LEDs in parallel and they worked fine.
On did fail after a year or two but the others carried on working fine until
I pulled them all and started using G4 COB leds.

I think you have what, 16 leds in all?
It would be quite doable to get some 680 ohm resistors and hook up wire
and do a bit of cuttery/hackery/soldery on the pcb and mod the thing
so that they all run in parallel each with their own series resistor.
A few spare ultrabright leds to replace any dodgy ones would help as well.

Just recalled:
I mounted the tail/stop leds on Vero/strip board when I did mine and it was much neater than having a rats nest of hook up wires
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bikers smell of wee

[Riejufixing]

Fixed: touched each dodgy-looking PCB-LED connetion with a pointy soldering iron, applied a tiny bit of solder, all work.

[MCN]

Lead free solder. Bastirt Stuff.

I got some Chinesium (lead tin) solder from Ally Express for this very reason.

Fcku them and their lead free pish.
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.