A BE400 CREW; DEPARTING PHX; TURNED TO THE WRONG HEADING; REQUIRING CORRECTIVE VECTORS FROM ATC.

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RWY 25 PHOENIX HOLDING SHORT. TAXI CHKLIST COMPLETED. I ASKED CO-CAPT TO BRIEF DEP. WE BRIEFED THEN WE WERE CLRED FOR TKOF. AT 1500 FT CO-CAPT SAYS AT 15500 FT TURN TO 075 DEGS. I REPLIED; 'I DON'T THINK THAT'S WHAT YOU BRIEFED; CHK IT AGAIN.' HE REPLIED; 'YOU'RE RIGHT; IT'S 1550 FT. HE SOUNDED CONFUSED. I ASKED HIM TO READ IT AGAIN. I BEGAN MY TURN THROUGH 140 DEGS. HE SAYS I WAS WRONG IT IS 240 DEGS. I READ THE WRONG RWY DEP. I IMMEDIATELY BEGAN THE TURN BACK TO 240 DEGS. AT 220 DEGS; THE CTLR CALLED 'WHERE ARE YOU GOING?' CO-CAPT REPLIED; 'I WAS TURNING TO 075 DEGS. I READ THE WRONG DEP.' THE CTLR THEN INSTRUCTED US TO TURN TO 210 DEGS AND LEVEL OFF AT 6000 FT. I THEN TURNED BACK TO THE L TO 110 DEGS. THE NEXT CALL WE WERE INSTRUCTED TO CALL THE WATCH SUPVR. WE HAD NO CONFLICTS; HOWEVER WE WERE TURNING THE WRONG WAY INITIALLY. HUMAN CONSIDERATIONS: IT HAD BEEN A LONG DAY. IT WAS LEG #4. I HAD CONFIDENCE IN MY CO-CAPT WHEN HE BRIEFED THE DEP; SO INITIALLY I DID NOT QUESTION THE BRIEF. AT 1500 FT WE DID DISCOVER THE CONFUSION. I QUERIED MY CO-CAPT; AND WE BEGAN CORRECTION; BUT IT SHOULD HAVE BEEN SOONER.