I do not think I have two rectangular connectors. The Scosche FDK-15 matches what I have.

What do you mean "low level output" from the factory head unit? I thought the factory amp has speaker level inputs???

Whatever they did, it does work.

1999 Contour Sport
V6 5 Speed
Sony 7050
Polk dx7 5x7 (nice)
Sony 12" so-so sub (150w RMS)
Sony XM552 (140W RMS) amp