Rear tail light??

[Lammer205]

Hi I have all lights working fine except rear tail light , can't figure any tips on what I need to look towards? Thanks

[Knowledge]

Have a check of the Earth. This is often the cause.

Try running a temporary earth from the engine casing to the rear end, just to prove whether this is the cause.

(Personally, I always run an earth cable through the loom to all locations, rather than use the frame as the return route for the power)

[Meds]

If you’ve done as knowledge suggested and haven’t cured it
Assuming you have Italian series 3 electrical system ( or derivative)
does your speedo bulb work ( this proves the power to the speedo/tail light circuit)
Does you brake light work (this proves there is a return path from the tail light.)

If both the speedo light and brake light work then the fault is most likely in the supply from the headset to the tail light unit or in the tail light unit.
Most common ( and likely ) are bad connections either in the headset or to the tail light
The connections in the lamp holder
The best method of finding this is continuity testing.

Don’t rule out a bad bulb - I’ve had new ones out the box not work

[corrado]

Don’t rule out a bad bulb - I’ve had new ones out the box not work

I'd check that first with a battery charger. Earth to main body of light and live to each filament in turn to check rear light and brake light.