The amp is for a music system?
There should be no arcing - not even a tiny spark - when this amp is
OFF. If there is a current draw when the amp is OFF then something is
wrong with it.
The amp should also have a fuse between it and the battery.
Read the amp's specifications, specifically how many amps it draws, and
install a fuse of that amperage in its power lead. I suspect the amp is
shorted but the only way to really know is whether a correctly sized
fuse carries the amp's specified load.
Attaching the amp directly to the battery means that anyone can play it
anytime the car is unlocked, the ignition key isn't needed to run the
amp. Do you want that?
However you arrange the amp's power be sure the connection is clean,
fused and tight.