Steering gear problem

HI GUYS...i have an 03 expedition 4x4 5.4l that i put a used rack in since i had put a new pump on it and it still didnt have any power steering. i got it all put in but steering starts to turn easy then hard then easy and so forth like its gettin caught on something binding up.its still in the air..i disconnect rack from intermediate shaft and there is no bind and the rack turns easy. i also messed up got frustrated and turned the steering wheel end tryn to figure it out and now the air bag light is on.:banghead: can anyone help m figure this out?