This circuit adds a nice fade-in fade-out visual effects when switching your in-car lights on and off. The fading time can be changed by adjusting the charging and discharging times of the capacitor. To do this, adjust the values of the 10 KOhm and 4.7 MOhm resistors.
BUZ74 is a SIPMOS power transistor (Siemens MOSFET) that can handle up to 500V. Instead of BUZ74, you can use any other power MOSFET that has a VDS value greater than 50V.