There is no factory crossover. The speaker cable splits in the door (I think) with one set of wires going to the tweets and the other going to the other "speaker".
Check out my SITE
, see if it helps.
You are bound to break a couple of the yellow popper clips, buy a handful from you local dealer.
I ran a Monster cable 4 pair line, two 12 gauge speaker wires and a 14 gauge remote power line from the boot, to the head down the right side and it worked very nicely. Getting the plastic panel below the door off and back was a huge PITA though.
Let me know if you need anything.