[Navy I.C.]

It's hard to tell w/out troubleshooting and elimination...

did it ever cut back on? sometimes undervoltage protection will kill the output.

and then you got the usual suspects; open, shorts, grounds, and fuses.

and then there's the rca's and the HU itself. I once had a problem with my HU's rca's outputs puttin' out way too much voltage, but it was cool 'cause everything was under warranty.