[ptlvr]

The only thing in my experience that would constantly cause that light to go on is a short I.E...wires crossed ,positive line touching ground,or vice versa.
Do 2 things look at the amp and make sure all your connections in and out are clean and not touching the amp hopousing itself just the terminals,then go to where the ground is mounted and make sure you have and extremely clean bare metal surface connection no paint or anything else there,this would cause ground to break and register as a short causing your light to go on.
One other thing maybe you said so and I missed it but what is your operating specs on the sub and amp and how high do you have tha gain set on the amp?