In the power distribution system in the engine compartment there is a fuel pump relay but also a fuel pump fuse. Why both? I have elementary enough understanding that a fuse prevents an amperage overload.

The relay is the “switch” so to speak that actually sends power to the pump. The fuse like you said provides protection against an over draw of current due to whatever problem may occur.

Wooley thanks. Not that I need an explanation, but I understand, say, you put a relay on your headlights so all the power doesn't run through the dash switch. Since there is no such switch for a fuel pump (on a passenger car) I'm assuming the low current side is for the computer.?

The control for the relay is the ecm. In other words the ecm is the switch for the relay.

Thanks, appreciate you taking the time!