Hi,
to control a FET you don´t speak of absolute gate voltage.
Allways refer the gate voltage to the source voltage. --> Voltage between gate and source --> V_GS
for the high current FETs:
* I recommend to use a resistor beween each gate and source. (instead of your gate circuit)
This ensures, that the FET is OFF by default.
To switch it ON:
use a n-Channel FET or a NPN to drive the gate LOW. (similar to your circuit at RA1)
Use a resistor to limit the the current, but ensure proper V_GS levels.
Mind that a light bulb will draw a multiple of it´s nominal current when cold.
Mind that car voltage may be very dirty .. with much spikes on the lines.
You need to protect your FETs from these spikes.
Klaus