Comunque mi ha risposto adesso (erano in vacanza)
E questo è quello che dicono:
I have asked the engineer. The problem as your description is canbus problem, so you need to add an extra canbus relay to solve it.
Because LED kit has smaller power than halogen bulbs, halogen bulbs are 50-60w but LED kit is just 20-30w, the car system will think it is a fault and make the light not work.
Relay is 6.5 usd for one pair