BGM LED rear light board problem

[Tractorman]

I thought I check my lights yesterday before the ride down to Burton Brewers rally. The back light on the scooter did not work, BGM LED board, so checked the power down to the light that was fine. Remove the LED unit and tested it on a separate battery and it worked OK so I put the original bulb unit back on the scooter and it worked fine. Put the LED back on still not working so I stuck the bulb unit back in and all works well. Anyone got any ideas what is amiss?

[MickYork]

does the brake light work ?

[citydaz]

I have one of these.
They can be a bit tempramental - if you push it in a bit sometimes it works and sometimes it doesnt.
I replaced the unit with a different one, and it has worked fine so far.

[Donnie]

ooof, so you needed 2 to make one work? how much are these?

[Vega125s]

Clean (emery paper) and check all connections .

[MK Monty]

Never had one of these but as I understand them, they can use AC or DC input. They must have some form of bridge rectifyer to convert AC. In your case that bits not working but with DC from the battery it works. I still believe anything running AC on a Lambretta will be subject to a high voltage fluctuation so I would be looking at the tracks and connections going onto the board look at any dull grey solder connections. Resoldering with fresh solder may help. A wassel DC conversion with a battery uses the battery to buffer the supply smoothing out the peaks and troughs

[Tractorman]

Never had one of these but as I understand them, they can use AC or DC input. They must have some form of bridge rectifyer to convert AC. In your case that bits not working but with DC from the battery it works. I still believe anything running AC on a Lambretta will be subject to a high voltage fluctuation so I would be looking at the tracks and connections going onto the board look at any dull grey solder connections. Resoldering with fresh solder may help. A wassel DC conversion with a battery uses the battery to buffer the supply smoothing out the peaks and troughs

Thanks for input, it is a DC system.

[MK Monty]

So it works on a battery by itself but not on a Dc bike, sounds like an earth fault, do you have a fuse on the bike battery, negative side? put a volt meter on the wires, does the BGM take its supply via the old bulb holder or is it wired direct to the loom e.g. Stop no tail with a good ground

[Tractorman]

It's a full DC system. On the original test the rear light did not work but the brake did, tested and found 12 volt to the rear light connection, removed LED unit and tested on separate 12 volt battery and found to work fine. Put it back on, still no light, fitted original bulb holder and bulb and all work fine.

[coaster]

Try running another feed to it whilst it's installed in the bike, if it still doesn't work then try running another earth. As Monty said, it's going to be a dodgy connection, remember that if you set you meter to dc volts you can test for high resistance joints by putting a probe either side of a connection. If the connection is good you should read zero volts, if you see a reading then that is telling you how many volts are being lost across the connection.