My amp is blowing fuses...

Lots of speculating going on here about the equipment I’ve run and how it was installed…

*I bought the amp from Best Buy back in 1997 with all new wiring.
*I installed it and haven’t looked at it in years…this is in my Mustang which only sees summer use so it isn’t everyday use.
*The gain was turned up maybe halfway.
*With the speaker wires disconnected and the radio off the amp will blow the 25amp fuse.

I have the amp removed, what is the best thing to do to test it? I was planning on removing the cover this evening to see if there is anything obvious.