Need urgent help

Ok a few years back I had Best buy instal an amp and sub...

Amp died (or so I thought) a few months ago. I finally ponied up and got a new amp.

Well today a good friend was helping me diagnose an issue...

The sub moves to the music, but not enough to creat any noise

We checked the sub, we checked the amp, we checked the um relay thingy (small black box that taps into the rear amp harness that you connect to the aftermarket amp)

Any way nothing was wroking. We pinned it down to the "relay thingy" by connecting another head unit to the amp and it pushed major bass. So I went and bought a new thingy and while installing it we noted super crappy installation by Best Buy.

Well after replacing it, still didn't work.

So question 1:

Any one have a clue what could be wrong?

Question 2:

Ok on the factory amp rack there are 3 plugins, we assumed the center one was setup for the Mach 1000. That's also where this relay was tapped into. Using a voltometer or whatever nothing is coming from this, but still feeds the amp enough that the sub vibrates to the music, but doesn't create any noise. We're thinking there's something in that center plugin that is fried.



I'm gonna take it to a professional installer (read not Best Buy), but I'd like to try to fix it with major assistance from my friend first. Also I can take pics if need be.

Single coil 4 ohm sub, all the parts are correct. The RCAs we used the external head unit to check. They're fine.

It's whatever that center harness is for. I'm assuming that it's a signal booster for the Mach 1000 subs (I don't have them). The inverter thing was wired into that center harness by Best Buy and they didn't hook the 2 brown (ground?) wires up, just the 2 white and 2 gray. We're assuming that's what caused the issue.

I had a RF amp, the new amp is a Kenwood KAC-8152D

When we used the external head the only thing we did was wire it through the existing RCAs, so that narrowed it down to the inverter or the connection. We re-wired the connection and I bought a new inverter. Same issue from factory head.

We were thinking about wiring the inverter into the drivers side Harness (that was the Bass and the right was Treble). But it still concerns me that the center harness is not showing on the voltmeter yet enough signal is going to the amp for the sub to attempt to move to music.

Well that's what I'm saying theres the passenger side and drivers side harnesses for the rear... Best Buy had it tapped into the center rear harness.

It worked for 3 years then just went bleah.

So is something fried on that center harness? If so is it important? Factory speakers work fine.

Also is it safe just to cover up the connections Best Buy made and tap into the Drivers side(bass controller) harness? (When I say harness I'm talking where they plug into the Mach amps)
Any pics would help, if I can have my friend re-wire it I'd be hapy not to pay another "pro" shop to do it)

Thanks Sonic, I'll point my friend to this thread and make sure I worded everything correctly.