To start off I'm replacing the transmission on a 04 bonneville gxp which has a 4.6l northstar with 4t80e transmission vin Y. So then I went to the junk yard asking for a transmission to a 04 Cadillac deville vin Y, being that bonneville gxp are hard to come buy. When I brought it home and compared the transmissions I noticed the connectors are different the bonneville gxp has 17 pins on the connector and the deville has 16 pins on the connector. Any help would be greatly appreciated.

Looks like you're in for a head ache. If I were you, I would pull the trans pan off (gxp) and try to trace down the 17th pin wire......what ever part it connects to, I would remove it, test it and install it into the Cadi trans. With any luck, it would be connected to a simple pressure switch of some sort.....and with more luck, the Cadi trans would have a removeable bolt plug in that same location that you can take out and install the gxp sensor......good luck.