Depress the rear brake pedal = engine cutout

[Herbert]

Dear all.
I'm looking for an explanation and remedy to solve this issue I have stumbled upon. Hoping you can help, please?

Here's the background:
Engine is a standard series 3 125 cc with a 6V, 4-pole Ducatti stator and points
The break switch is a single (pink) wire unit and is new
The rear bulb is a dual filament 6V 15/5 W which is held in a bulb holder forming part of a Carello lamp unit
Two earth leads from one of two terminals on the bulb holder are coupled to the two bolts holding the rear lamp unit to the frame.
The two bolts are linked together via what looks like an earth strip.

The brake light has worked perfectly well. However at one point, the larger filament of the bulb 'blew' and although the smaller filament continued to work, once the brake pedal was depressed, the engine cut out. I restarted the scooter a good number of times to see if the issue persisted and it did.

Any advice would be well received.
Many thanks. H.

[ladsdad]

Hi
I had this same problem a few years ago , sounds to me like your flywheel's magnetism has become weak & your lighting circuit can't cope when you load it by lighting your brake light. Try a different flywheel if you have one.

Mark.

[Herbert]

Thanks Mark.
I do have a second flywheel and will try that at the weekend.
H.

[Sticky]

Ladsdad might be right, but also try to replace the bulb first with the correct wattage replacement. Vespa smallframes with a similarly odd brake wiring system also suffer ignition faults with a blown brake light bulb.

[Herbert]

Thanks Sticky.
I shall try a 6v 15/3 W bulb.
all the best.