PWM output, how does it work?

[07-EDM-STI]

I've read that a stand alone ecu can be used to control water meth injection system, I don't know how the PWM works. does it work by pulsating the 12V output to control the meth pump? Can the PWM output of motec be connected directly to the 12V supply of the meth pump or does it need to be connected to a relay first to handle the high amp demands of the meth pump?? thanks in advance

[IJ.]

PWM>Solid State Relay>Pump.

[07-EDM-STI]

PWM>Solid State Relay>Pump.

thanks a lot