Rear light doesn't work anymore :(

[Bigsharn]

Hi all, the dynamo wires came out of my back light (which is fair enough, it happens), I put them back in and reattached the light for it to still not work!

I've tried swapping the wires and still no joy, the bike's made of aluminium so I'm guessing if there's a break in the wire somewhere it should still conduct (the wire goes through the inside of the tube).

The front light is still working from the same dynamo so is my bulb dead or could it still be the wiring?

On a sidenote I bought the bike in November with the lights attached, so if it IS the light it'll still be guaranteed. Will I need to send the light back or the entire bike?

Thanks in advance
Sean

 

[chillyuk]

Have you checked the earthing of the lamp. You say wires, plural, so does it have two wires feeding the lamp, or one wire feeding the lamp, then another from the lamp to the front light, using the bike frame as a ground return. The filament of the bulb is often clearly visible and can be checked visually for a break, although it can look good but be open circuit. If you have a test meter fault finding these things is a two minute job.

 

[Bigsharn]

It's an LED rear light so you can't actually see the filament. There's a positive and negative wire going into the rear lamp. I don't have any electrical equipment to test the connection either, as I say the line physically goes through the bike's tubing, so to see if it has a break in the line I have to pull the wires out of the tubing to check it, hence asking on here

 

[chillyuk]

Fair enough. Without a meter and unless you can see the fault it is a matter of trial and error. You can get cheapo meters good enough for simple fault finding for under a fiver (I have seen them in the pound shop occasionally), may be worth an investment.

 

[tyred]

If the headlight works with the tail light connected, it can't be a short circuit as a short circuit should pull the head light down too.

Check the connections are clean, dry and corrosion free at both ends. Even without a meter, you could test for power at the rear light by holding the wires on to the contacts of a 6V torch bulb and getting someone to spin the wheel. If there is power, the bulb should glow, and if this is the case, it does look suspiciously like a fault with the tail light itself. Or if you have a bit of light twin pair wire (speaker wire or similar), run it temporarily direct from the dynamo to the tail light and test again.

The wire which comes with most dynamo lights is ridiculously fragile and easily damaged in my experience.