Hey fullmetaljacket,

the chance came faster then expected. Changed one bulb with a T10 LED bulb (I believe that is the size which is in there) - all fine. Changed the second one - as you said. They flash for a second and go out then. Strange ... !

I assume we need to connect a resistor in parallel.

Original a 6W bulb is in.
I = P/U = 6W/12V = 0,5A
R = U/I = 12V/0,5A = 24 Ohm

So a resistor of 24 - 25 Ohm and a power of max 10 W would behave like the original bulb. It has to be connected in parallel to the bulb and it has to be isolated because it will become hot. Res: RES 24 OHM 10W 5% WIREWOUND - SQP10AJB-24R

Guys: school is over since a long time - if you find an error in that maths please do not hesitate to correct it.

Thanks, H