This seems to be a common problem with any ford that has these factory units. As I have a '03 Sport Trac I put mine here.

Around 2 years ago while I still had the factory 6 disk cd changer in my truck the subwoofer one day just quit working. At first it would stop for a while then come back for a bit and cycle like this while driving. It was a hot summer so I wrote it off to overheating. One day when it didn't turn back on I gave a quick inspection to the system and figured the amp had just fried. For the next year or so I left the factory head unit in and swore every now and then I would hear the sub kick in for a short time. I eventually gave up on that idea after having checked it many times and seeing the speaker not move.

I installed an Alpine head unit I have owned for a while, but had never bothered to install in my sport trac about a year ago, at the time I used a wiring harness that didn't support the factory sub because it wasn't working. Yesterday I got a wild urge to try and resurrect the sub and figure out why it died. After buying and installing the harness to connect the factory sub to aftermarket head units I got a friend to test a few things with his ohm meter. The power and remote both put out power (didn't realize at the time the remote feeds the power so if one works they both do), the meter ohms out when testing using the proper terminals on the amp, and both amps channels put out a signal. So that leaves one thing, a blown speaker. Wrong! after messing with the speaker a bit it turns out its simply a bad connection on one of the speaker channels between the wire hookup posts and the voice coil. In my case I will identify the channels by wire colors. One one side is red and wite other is blue and white. My speakers red channel positive connection simply started coming apart.

I haven't quite done the final fix yet as I need to revive my soldering abilities before I truly fix it. For now the wire is held firmly to the terminal by a piece of electrical tape. I do intend to eventually take a soldering pencil and carefully reattach the lead to the terminal.

So before you go cursing your ford factory sub and throw it away check everything you can. It may not often be the same issue causing a sub to fail but I will list some of the things I discovered with my specific system that are worth checking. My truck is a '03 sport trac xlt that had a factory Pioneer 6 CD Changer and factory 6" sub/amp. Firstly, the radio system pulls power from a own fuse located in the case of my truck in the distribution box under the hood. If your radio turns on this fuse is fine. At this point the remote line on the radio provides 12V power through a fuse in the dash fuse panel then back to the amp splitting just before the amp into a remote and power wire. It's a good idea to check this fuse, it is number 11 or the 2nd fuse from the right 3rd row from the top 15A mini fuse. At this point if you cannot resolve the problem you'll need a bit of electrical knowledge and an ohm meter. Test the leads coming out of the harness on top of the amp and see if they push power with the radio on. Then check the amps output again with the radio on. If all is good there continue to the speaker. Unplug the bottom connection and test for a circuit connection on both channels (in my case there are red and blue hot wires and 2 white cold wires each pair going to a channel on the speaker). I can't walk you through perfectly, this is the part I called in the friend on, however; I am sure the internet has information on how to do this. Play with the connections a little as you test. If you can get the meter to ohm out on both channels the speaker will still work you will just need to figure out exactly which connection is going out and fix it.

Note with an aftermarket head unit. As I have found from some research if you put an aftermarket unit in you are going to get a "pop" sound from the sub when you turn the radio on. This is due to the amp only running on 6V power but being fed 12V. The solution is to add a 1.5K ohm resistor in line with the remote wire. This reduces the flow of power on the line to 6V. You will lose a little power, but the speaker will not make a loud popping noise when the radio is turned on.

 

I am replacing my pioneer unit this weekend and from what I am reading I will be able to use the factory subwoofer with a new radio harness . From everything I have been reading it says I will lose the factory sub and have to run a wire to the front speakers