Stereo & Electronics - Subs not playing when RCAs fully plugged in

I am connecting my amp to the subwoofer output on my HU. I have the wires fully plugged in to the HU outputs. When I plug the RCA cables all the way in to the input of the amp, the subs do not play. When I plug them in just enough for the middle wire to touch the inner ring on the amp input, but the outter sleeve not touching, the subs play fine.

I really have no idea what would be causing this. If I plug the RCAs into the line out ports on my HU instead of the sub out, they play fine. I'm not sure if maybe the subwoofer output is bad or what.

Any ideas?

The HU is a JVC KD-LH300 if it helps.

Thanks

Any ideas?

The fact that it plays ok when only the center conductor is connected, sounds like your HU has a bad ground on the sub channel. IF it's new, and you can get it exchanged, I'd try a new HU. IF not, and you can live with using AUX channel, you can just use that.

switch the rca cables to connect it the opposite way so if the ones that went to the stereo now go to the amp try that first.

sounds like a normal problem when you buy jvc