Now it works, now it doesn't...(Sub/Amp)

I know you guys like a challenge with an ambiguous diagnosis, so how about this one. My sub worked last year, now it doesn't. The Alpine Mono amp that goes to it lights up. I think that means that remote lead and power/ground are out. I have freshened the tips of the speaker wire at the box terminal and speaker, but not the amp. I have a WS420 in line as well. I have swapped RCAs, and that did not help. So I am thinking run a speaker wire straight to the box and check that? Otherwise, it is something internal in the amp? Thoughts?

Thanks in advance!
Jason

Are the batteries fully charged? Is the sub volume knob on the EQ tuned down? On most amps, the lights and their color mean something. Are the lights and the color indicating normal operation per the manual? Do you have a volt/ohm meter? If so, then pull the sub wires from the amp and test it for a compete circuit. Lay in a set of RCA cables directly from the head-unit to the sub amp and bypass the EQ.