What could be the problem?

I installed my Clarion CD deck, my Pioneer TSW300R 12, and my Power Acoustik PWR 180 amp today. The deck is out of my old truck that I wrecked, but I never used the RCA outputs on it before. The amp is one my brother gave me, but he never used it in the time he had it. The sub is brand new. Here's the problem, though. My sub is making barely any noise. If I unplug my door speakers and crank the deck, I can hear the sub and it pounds pretty good. but if I plug the door speakers back in, they drown out the sub at a regular level. Any ideas on what the problem is? There's two sets of RCA outputs on my deck, and the problem occurs with both.

Do a search on gain setting.My ex once told me I have a perfect face for radio.

Could be any one or any combination of the following: incorrect amplifier gain, low or off subwoofer level from HU, crossover set too low, bad RCA cables, bad head unit, bad amplifier, bad subwoofers.  I'd begin by making sure the signal level from the HU is sufficient and the amp gain is set properly, and make sure the sub amp LP filter is set to 80-100Hz.Support the12volt.com

I don't think it's the gain. Turning the gain down all the way just makes it almost entirely inaudible. The further I turn up the gain, the louder it gets, and at max, it's still extremely quiet. What's a sub amp LP filter, and how can I check the signal level from my HU? Also, the only piece of equipment I would expect to be bad is the amp, but I'm really hoping it isn't.

UPDATE: I just played with it for about an hour and in a desperate measure after trying everything I could think of that didn't involve removing the deck, I tried something weird. I left the sub hooked up, bridged across both channels, and I unplugged both RCA plugs. Then I put the L in the R jack. It pounded hard as hell for a few bass hits in the Jay Z song, and I immediately unplugged it. Did I just ruin my sub? I'm so confused. It can only pound too insanely hard or not at all.

Try running a new rca cable from the front to back. Some amplifiers when bridged also take only the left channel input to get it's signal from. There may be a chance that the rca cable was bad on the one channel and when you moved side to side, the good side of the cable brought it to life. Turn the gain back down and test again.Top Secret, I can tell you but then my wife will kill me.

Is it safe to test it that way, even with the gain down? The gain was all the way up at the time, because as I mentioned before, barely anything comes out unless it is. That RCA cable was $20, so I hope it isn't bad. I guess I'll keep trying this cable unless I can verify it's definately bad. It's also in cable conduit that is underneath my truck's plastic molding. That's gonna be a bitch to pull up again.

Ok, in my excitement last night that I finally had some real sound out of it, I failed to realize it was just one big thump and then a smaller one, nothing from the music. I tested it some more and it continued to thump once really loud, then go back to playing at a barely audible level. It does this with the left or right channel audio cable plugged into the right channel jack.

My sub is SVC, and wired correctly as far as I know. There is no way to adjust my subwoofer level on my HU, it gets adjusted with the door speaker level. My amp has no low pass filter, just a gain adjustment.