Vespa 50 N Sip speedo/Polini 12v ignition turns off with lights on

Hi guys, i'm on it for a week now and i've made as much research as i could.

The speedometer is working perfectly without any other connection (Headlights/Rearlights), show temp/rev/kms...

AS soon as i connect it, even with one single 5w 12v rear light it turns off...

 

I've changed my wire entirely, i've a Polini ignition 12v and the wire is perfect.. i've also tried to run is at 7000 rpm and only 6v lights... Not working.

Now all the wires are new and this is the same issue...

Even my father which was an electrician engineer checked everything and don't get it..

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Any ideas ?