If your power and ground connections on your amp are very close together than it is possible that a couple strands of wire from your power are touching your ground terminal. If this is the case then fix it as soon as possible. If it's just a couple strands then i may not be large enough to cause your fuse to pop but could cause the wire to get hot and possible melt the sheath. I'd disconnect your wiring, clean up the stripped ends and reattach and see if that fixes it. If not then there could be somethig worng with the amp internally. assuming that your ground connection is good. But i don't think that a weak ground would cause it to get hot. Electricity is what is makign the wire hot and a ground should always be ground (good connection or not) so I think that somehow your ground wire is carrying current.