A B777 ON TKOF ROLL HAD MAIN GEAR STEERING WARNING LIGHT AND HORN WITH MESSAGE WARNING LIGHT. CAPT ELECTED TO CONTINUE TKOF AND AT V1 ALL WARNING LIGHTS WENT OUT.

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AT XA35Z WE WERE CLRED ONTO RWY 30 IAD. AS WE WERE TAKING THE RWY; WE WERE CLRED FOR TKOF. WE WERE HAVING AN ENRTE CHK BY WX WXXX THIS TIME. AS I ADDED PWR FOR TKOF; THE MAIN GEAR STEERING WARNING LIGHT AND HORN WENT OFF. I IMMEDIATELY STARTED THE PWR BACK AND THEN NOTICED IT WAS THE MAIN GEAR STEERING WARNING LIGHT. I HAVE HAD THIS WARNING LIGHT A FEW TIMES BEFORE; INCLUDING ON MY IOE AS WELL AS TRANSITION SCHOOL IN THE SIMULATOR. BOTH TIMES; THE GUIDANCE I RECEIVED WAS TO CONTINUE AS THE LIGHT WILL GO OUT AS THE TRUCKS STRAIGHTEN OUT. USING THIS INFO; I REAPPLIED TKOF PWR ANTICIPATING THAT THE LIGHT WOULD GO OUT. AT THIS POINT; I WAS WELL ABOVE 80 KTS AND WITH EMPHASIS ON NOT ABORTING UNLESS A NON FLY SIT OCCURS; I MADE A CAPT'S DECISION TO CONTINUE THE TKOF; AS ALL OTHER SYS WERE WORKING NORMALLY. AT V1; HORN/WARNING LIGHT ALL WENT OUT AND THE TKOF WAS OTHERWISE UNEVENTFUL. WE CALLED MAINT AND BRIEFED THEM ON WHAT HAPPENED AND RECEIVED A RESPONSE TO TAXI/PARK VERY CAREFULLY. FYI -- THIS ACFT HAD NUMEROUS WRITE-UPS: INOP AUTOBRAKE SYS; FUEL GAUGE PROB; APU MUST BE LEFT RUNNING; ETC. WXXX COMPLETED A DEBRIEF.