Waterfall pump hums but won't pump

It might have some worn parts inside, like the bearings, or bushes

UNPLUG PUMP AND SEE IF THE IMPELLER IS JAMED, IF IT SPINS FREE TRY IT WITH A SHORT DISCHARGE HOSE. POSSIBLE BLOCKAGE IN DISCHARGE HOSE WILL TRAP AIR AND WONT LET PUMP PRIME.

Sounds like there are too many things running on the same breaker. Try unplugging some of the other things on that breaker.

Fuel pump won't be the cause. Most likely the relay.

since this is a waterfall pump , id try using a short piece of dish hose and see how it flows water then , if it works there then id say your demand to lift is too great and a larger pump will be needed to lift that high ,

also note on waterfalls id leave out the ck valve on dish pipe , i know it takes longer to reprime itself each time , but that reverse flow action cleans your intake screen each time it shuts off

Go under the dash and bypass the clutch pedal safety switch and see if it starts.

Clogged, Impeller loose and not turning. Remove strainer from bottom of pump and check for clogg and see if the impeller is turning.