Amplifier problems?

Hi all,
Got a small 10" apline subwoofer in my wagon that's run from a 100w amp.
Anyway,
The amp fully works on the bench with sound coming out to a little speaker I've wired to it,
The alpine sub fully works, tested with an AA battery and it crackles & pops, it's been working fine the last 6months odd with the amp.

All of a sudden it stops working.
So I've tested them both on the bench,

When I install them, the amp powers on like normal but there's no sound going to the little speaker or sub.

I've got my phone as the input direct into the amp so this rules out the headunit,
Live, earth and remote are all on and good,
No sound output from the amp??

If i take it off and test it on the bench plugged into a mains 12v power suply it works with sound playing??

I'm really lost here?
It's like it's not getting enough power but the battery is on 14v when engine running and still nothing.
Any ideas would be great!
Thanks again..

Is all well now,
Turned out a solder inside had broke off, when it was flat on the workbench it touched when I fitted in my wagon on its edge it would come away from the board and not work.