harness location or 4.6/ wapping out the 3.8

[mikes97sn95]

i have a 97 s speed v6 (3.8l) i purchased a full motor tranny and engine wireharness from a wrecked 97 gt. what im needing to know if i can drop motor in connect gt engine harness right there at fire wall and install gt computer under dash. or is the wire harness that runs from firewall down to the ecu have to be from a gt as well. and if so does this harness run from firewall to ecu or does it include all the lights and horns and other stuff on same harness. i tryed to trace it but wasent ready to pull my finder and bumper off to track it down. can anyone help? please