Scooterotica

As an ex-electrician, I'm normally pretty good with circuits etc (just made my own 2nd DC loom for LED indicator system etc & it all works a treat) but this one has really got me stumped!
Just doing some testing of my lights (using a battery feeding to the brown reg cable) prior to putting engine in and I've got a strange problem that I just can't fathom.
Head (dip & main), pilot & tail all work as they should via a new SRS ignition switch (2nd position).
When the lights are on, brake lights (F&R) work perfectly but with the lights switched off, they don't.
If I disconnect the tail light wire at the rear lamp unit, both brake lights work perfectly irrespective of whether the lights are on or off (as they should).
As soon as I reconnect the tail light wire, the brake lamp only functions when lights are switched on.
In practice it's probably not an issue as I ride with my lights on anyway but I'm more concerned that
Mr MOT man will fail it as technically with lights off & engine running, it has no brake lights working.
I'm good with electrics but I am totally baffled by this and tearing out what little hair I have left!
I'd be grateful if anyone can suggest anything to look at - PLEASE!

hi, had a similar issue to this on my series 1, i was running a bgm 'type' rear led light/brake light & the brake light would only function with the either the side light or main lights switched on ! switch the lights off & nothing ! the only way i fathomed it out was to fit the original bulb holder & bulb & then it all worked normally !i have since changed the led rear light for a different type & since then have not had this issue again, i know this isn't quite the same problem as your having but hope it helps in some way . good luck db67

Funny you should mention that as I'm using an LED rear light too (Rich Presley one).
I haven't tried swapping it for the originalbut I might try that just out of curiosity.
I can't see why the LED board would behave this way though but it's odd you had same issue.

Update! And db67 you're right.
Just temporarily swapped the LED board for the standard bulb holder & it all works correctly irrespective of whether the lights are on or off.
I'm happy that my circuitry is obviously correct but I still don't understand why this should happen so maybe an appeal to the electronic experts now 'cos that's not my area of expertise!

no problem, glad you got the fault sorted mate ! could be that you have a dodgey led light board too ! if its not that old then maybe see if rich will exchange for a new one,he seems a reasonable enough bloke db67

Leds need to be biased on unlike bulbs, try fitting a 470ohm 1/4watt resistor in the positive supply line to the board, this may help, it worked for me

db67 wrote: could be that you have a dodgey led light board too ! if its not that old then maybe see if rich will exchange for a new one,he seems a reasonable enough bloke db67

I don't think the board is faulty - if I connect it direct to a battery it works fine on tail & brake.

essexgp wrote:Leds need to be biased on unlike bulbs, try fitting a 470ohm 1/4watt resistor in the positive supply line to the board, this may help, it worked for me

Cheers for that - would that be in the POS feed to the tail or stop circuit (or both)?

~Try it on the supply line to each one first and see if it stops it if that doesnt try to both, as i said worked on mine

essexgp wrote:~Try it on the supply line to each one first and see if it stops it if that doesnt try to both, as i said worked on mine

Cheers for that - I'll give it a go.