2000 Navigator Sub Wiring Colors

Personally, I wouldn't put ANY aftermarket sub into the factory location AND use the factory amp...

First step is to ditch the factory amp and get a nice aftermarket one.  I'm willing to bet that factory amp will HEAVILY underpower that MTX sub, which in turn, will blow it...

You can still use that factory location (with probably a few modifications), but don't use the factory amp.

I've done that before back in my green(er) years.  I had a '89 Probe with a 5" factory bazooka-style sub...when that finally gave out I used a home 15" sub, built a vented box for it without even measuring or understanding what I was doing (I used a heavy cardboard tube for a port ...lol)....put that in the rear hatch...connected to the OEM sub wires...result was deeper bass response than I had with the factory sub but only a little bit louder.  Just as well because I could have quickly ruined the home audio sub with more power, being in a incorrectly designed box.

You won't harm the MTX sub by connecting to the factory sub amp output...underpowering will not blow your new sub.  If anything, depending on the impedance of the new sub, you could end up frying the factory amp.  But if the MTX impedance is 4 ohms you should be okay.  The results might be quite a bit less spectacular than you hope for, and in fact the factory sub might even be louder and sound better.  It's a classic example of properly matching up amp/sub, etc. 

As for the two wires, you will never hurt anything by connecting the polarity wrong to a speaker.  If you put the wires on incorrectly the sub will play out-of-phase with the rest of the speakers, resulting in little output.  It's best to try it both ways and use what gives you the loudest bass response.

And yes, a new dedicated sub amp is in your future.  After that, you'll most likely want to upgrade everything else as well.

Steve - Thanks for all of your help.  Glad to hear I won't mess up the sub if I pick the wrong speaker output wire.  As far as the amp is concerned, I do have a 450 watt MTX amp to go with the sub, but I'm having issues with the speaker-level input to the amp - it makes the speakers cut out (see this link: https://www.the12volt.com/installbay/forum_posts.asp?tid=55346&PN=1).  A line-input converter was recommended.  I am going to try that and see if it works.  This is incredibly frustrating.  I would ditch the factory HU, but I really don't want to lose the operation of my steering control buttons and the integrated factory CD changer in the center console.

Thanks for all of your help.  This is an education to be sure.

Tom