I've done everything I know to do and I still can't get the answer. I went to install an aftermarket audio/video/nav unit in my 2002 Mercury Mountaineer. The truck has what the manual calls the "Audiophile" sound system which includes a subwoofer. I have a Chilton's manual with wiring diagrams, but it only shows the "base" sound system. After spending the last three hours on Google (see, I looked before I asked), I can find lots of wiring information, but again, only for the base system, not the Audiophile system with the subwoofer.
Based on my searching various sites, including companies who make connectors for aftermarket audio that plug into the OEM connector on the truck, here is what I think is the story, maybe somebody can confirm it. I believe that the 16 pin connector has the speaker outputs, but that the amplifier for four right/left/front/rear speakers is contained in the head unit (just like my wiring diagram says it is for the "base" sound system) and not a separate amp. Therefore these require an amplified output from the head unit (my new head unit has both line out and amplified). I believe that the 8 pin connector, which only uses four wires, one of which is an uninsulated bare wire, is for the powered subwoofer and connects to the subwoofer amp. This would make sense as I'm guessig the four wires are: Signal, ground/shield for signal, power, ground for power (or maybe a trigger). Therefore, this would connect to a subwoofer line out, power and ground. In fact, the after market connector which the company who makes it says works for my truck, has the 16 pin connector and a separate RCA connector, which also has two other adjacent wires. The subwoofer line out on my new head unit is in fact an RCA connector.
So what I'm thinking is that the 16 pin connector is the same on both the base and audiophile versions and the wiring it connects to is the same as well, and that the only difference is that audiophile version adds the 8 pin connector, using four of the pins for an added amped subwoofer. If you know, please let me know. Thanks in advance.