Cummins ISB 5.9 Cranks but no fire-ECM power.

there aretwo power sources to the ecm one is from the ignition switch and the other is unswiched ( hot all the time ) usually connected directly to the starting batterys this wire will have a inline fuse ussually in the battery box make sure it's not blown. if you had the cables disconnected did ths wire get reconnected a quick check to verify the ecm is powering up on initial key on the check engine and stop engine light should cycle on and off if they don't either the swiched or unswiched power is missing

hope this helps