What was found
CREW REPORTED "NW STEERING DISC" MESSAGE AFTER TAKEOFF AND GEAR RETRACTED. NOSEWHEEL STEERING NORMAL DURING TAXI OUT AND INDICATION DISAPPEARED AS USUAL WHEN PUSHBACK CREW REMOVED BYPASS PIN. AIRCRAFT DIVERTED TO CLT, CREW DECLARED AN EMERGENCY AND LANDED WITHOUT INCIDENT. AIRCRAFT WAS ABLE TO TAXI TO GATE UNASSISTED. MAINTENANCE FOUND NOSEWHEEL STEERING DISCONNECT BOX TO BE BAD. - REPLACED BOX. ALSO REPLACED BRAKE STEERING CONTROL UNIT. VENDOR INDICATED REMOVAL WAS JUSTIFIED - UNIT FAILED FUNCTIONAL TEST DUE TO LIGHT BULB CORRODED AND WORN CAMSHAFT & COVER PACKINGS.