CDI dies when earthed

[vegansydney]

I have just fitted a new (genuine) Ducati CDI and as soon as I earth it via the yellow wire, the CDI stops sparking. As soon as I disconnect the earth it has a big, healthy spark again. Any thoughts before I pull flywheel? Never experienced this before.

Thanks in advance!

[dickie]

Assuming ignition was OK before you changed CDI and that you've wired it correctly, there's an internal fault where a potential is connected to the CDI ground.

I'd try another CDI before pulling the flywheel.

[missing lynx]

Isn't the yellow the feed from the stator?

[dickie]

Isn't the yellow the feed from the stator?

Good point. It is normally. White is earth on the CDI, isn't it? It's so long since I've used a standard one that I've forgotten the colours

[Fast n Furious]

I have just fitted a new (genuine) Ducati CDI and as soon as I earth it via the yellow wire, the CDI stops sparking. As soon as I disconnect the earth it has a big, healthy spark again. Any thoughts before I pull flywheel? Never experienced this before.

Thanks in advance!

Best to identify what flavour of stator plate you have here to determine what colour wire does what.
Usually:-
Yellow = lighting supply to the regulator.
Green = 200v LT supply to the CDI
Red = Trigger pulse to the CDI
White = Earth strap from the stator to the CDI

Some original SIL AC stators were:-
Brown = lighting supply to the regulator.
Green = 200v LT supply to the CDI
Yellow = Trigger pulse to the CDI
White = Earth strap from the stator to the CDI

Some regulators also had a short integrated yellow wire which was also a ground connection.

[Wack]

The yellow is not needed provided the stator/engine has a good earth to the frame. Basically the yellow is just an internal connection to the white terminal and can be checked for continuity.

[vegansydney]

Thanks for all the advice! Very much appreciate it.

To clarify, the yellow wire is the earth wire off the Ducati CDI, not the stator. Sorry for any confusion!

FYI: the stator is later BGM DC with the black earth wire. I've earthed one of the yellows off the DC stator to run on an Italian-market Special without battery tray. Loom is an older MB simplified harness.

I swapped the CDI out for a genuine Ducati blue one, as the red BGM one that was previously fitted died on a ride. Had spare Ducati on me and swapped it out, zip tying it in place temporarily to get back. Once back in workshop I fitted it correctly to SLJ mount and noticed spark was non-existent when it was earthed. As soon as I disconnected the earth the sparking was back.

[vegansydney]

The yellow is not needed provided the stator/engine has a good earth to the frame. Basically the yellow is just an internal connection to the white terminal and can be checked for continuity.

Good to know. There are good earths between engine and frame. Thanks!

[Fast n Furious]

try using a multimeter to see which of the connector terminals are common with this floating yellow

[vegansydney]

try using a multimeter to see which of the connector terminals are common with this floating yellow

Will do, thanks!