1998 with Kenwood BT945U rear speakers

Need some help with figuring out how to connect the rear speakers. I bought this awesome truck in late Nov and the previous owner had put 4 speakers in the back of the seat. The front speakers work just fine. I am looking forward to figuringo ut how to connect the rear sets. maybe 2 are subwoofers? the only think I do know is there is a big white wire that runs from the front underneath the carpet to the back speakers and he does have 2 wires labeled. rear left and rear right. there is also a big black and blue wire that is not connected on one end (guess maybe he had that attached to an "amp" - or something? and almost connected to the other back speakers. I can check the colors later..but yesterday I noticed the 2 speakers that did have connections only seem to have them on 1 side of the speaker connect. I hope this makes sense. I can get some more info later and some photos.

is there anyplace i can find a wiring diagram that might help? thank you