Hi, allready thx for the answers.
wiring diagram is
here
the problem seems to be solved today... will check my battery later today.
alternator is only 3 months old (110Ah, the old one was only 70Ah) and my battery is also only 3 months, so i doubt that wass be the problem...
anyway, my usb devices stay powered, but i do not think they draw a lot of power... (steering wheel controls are not powered via the pc, radio is not connected at this time, touch screen is shut down)
If the problem comes back I'll let you know...
Greetz
Dj NRG