Hey, thanks for the quick reply
I thought about the logic level mosfet too (I couldnt find the specific datasheet for my mosfet, but a similiar one indicates what you said with the 10v).
But why is it working with the LED then? Nevertheless I will buy myself a new correct mosfet.
Its working with the LED because that's a low current load - the MOSFET only has to be less than a few 1000 ohms to
light up an LED convincingly. To turn on a 12V bulb (which might take an amp) requires it to drop to a fraction of an
ohm (its rated as 0.4 ohms with 10V gate drive, which would work, but its not very good).
High voltage MOSFETs have much higher on-resistances than low-voltage ones, for instance this one is 200V and 0.4 ohm, whereas a
beefy 30V MOSFET might be anywhere from 0.02 to 0.002 ohms these days. If you want to switch 12V, use a MOSFET with
a rating in the 30 to 50V range, logic level and expect the on-resistance to be somewhere around 0.02 ohms.
In fact work out the current you need to switch and use I-squared-R to calculate how much power a possible MOSFET
will dissipate - this will help you choose the right device and decide if a heat-sink is needed.