do i need take wireharness off 2000 ram 1500 4x4 for a 1998 ram 1500

i have a 1998 ram 1500 2 wheel drive putting the cab and the bed on a
2000 ram 1500 4x4 all match didnt touch motor or anything just switch the
cab and bed i switch the computers around but not the wiring harness now
i can get the truck to start or turn over again did nothing to the the motor do
i need switch the wire harness i did the one under the fire wall just not the
one in the truck if not does anyone know why it wont start or turn over i do
hear the fuel pump when try to start it