I have just a few simple questions about PWMs.

My car outputs 13.8 Volts. Does that matter?
Does a PWM help limit the amps going into the device?
What the hell is a frequency adjuster? What does the frequency have to do with amps and volts?
Whats duty cycle Range?
And I know spades are not good in PWMs, so what should I look for other than spade connectors?

Thanks in advance guys