ACR CAPT REPORTS CONFUSION USING THE PARKING GUIDANCE SYSTEM AT DFW.

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TAXIING INTO PARKING AT GATE; PARKING SPOT HAS 2 LEAD-IN LINES. STARTED TO TURN ONTO WRONG LEAD-IN LINE. PARKING GUIDANCE SYS DID NOTHING TO PREVENT ME FROM STARTING DOWN THE WRONG LINE. AND; IN FACT; AFTER I WAS LINED UP ON WRONG LINE IT GAVE INSTRUCTIONS THAT INDICATED I WAS IN THE CORRECT POS AND I FOLLOWED THE INDICATOR TOWARDS THE PARKING SPOT. ABOUT 1/2 WAY FROM THE ENTRY SPOT TO THE PARKING SPOT; I BEGAN TO GET THE RED ARROW CORRECTING MY MISTAKE. THIS TIME I ENDED UP WITH MY NOSEWHEELS ON THE CORRECT PARKING SPOT FOR MY TYPE AIRPLANE BUT THE BODY OF THE ACFT WAS DISPLACED TO ONE SIDE. AFTER DEPLANING I CHKED THE SAFETY ZONE. THE WINGTIP ON THE SHORT SIDE WAS ON OR WITHIN THE SAFETY SETBACK LINES. THIS IS ANOTHER SHORTCOMING IN THE DESIGN OF THE PARKING GUIDANCE SYS. CREWS NEED TO BE WARNED THAT THEY ARE STILL ENTIRELY RESPONSIBLE FOR SELECTING THE CORRECT LEAD-IN LINE; THAT THE PARKING GUIDANCE SYS WILL NOT WARN THEM OF THEIR ERROR. THE PARKING GUIDANCE SYS SHOULD BE RE-ENGINEERED TO PROVIDE SUCH A WARNING. IT SHOULD BE ABLE TO DETECT THE ERROR AT THE FIRST FOOT OF THE LEAD-IN LINE TO THE PARKING SPOT AND IF IT CAN'T SEND A WARNING MESSAGE TO THE CREW; IT SHOULD CEASE OP.