i had a bose system in my ride with 4 wires to each speaker. 2 wires were power for the amp (at each speaker) and 2 were signal wires... maybe noting the coloring of the wires back from the factory side of the harness will help you know which 2 are the ones you need to use.
:ons Firesuit:repares for n00b initiation::hopes not to be cotjones::
I think you could probably disconnect the factory harness and figure out if you have power wires or signal wires by DMMing each of the wires to a good ground and a known +12V. I figure signal wires would give you nothing, a ground wire to +12V will give you 12V, and a power wire to chassis 12V... That is just a guess, and if I'm wrong I'll probably get corrected quickly...
If it did have a seperate tweeter, I'd just try one set of wires then the other. One should be obviously lacking bass (the set u don't want). Hopefully it's like the diagram, and it's crossover is just a HPF for the tweet, and no LPF for the woofer.