ok first question:
Can i use a transistor to turn on a fan for my amp. I have a constant +12V, a power wire from the radio and of course a ground. Would a transistor help me at all?

second question:
I have VATS (duh i know) but i also have some sort of keyless entry system. (one button locks and unlocks doors and the other pops hatch). Under the dash near the fuse panel is the big block for the electronics for it. but coming away from it are a couple wires going to a toggle switch. its just a basic on/off one like you would see on airplanes from old movies. can someone tell me what it is for? i cannot notice anything from moving the switch. (fuel pump,lights, and keyless entry all work in both settings)

 

#1) It would have to be a big transistor (amp)

#2) Someone added that switch, its not factory.