DO328 CREW TURNS TO THE WRONG HEADING AT BYGEC ON THE BRAYMER 3 INTO MCI AFTER MANUALLY LOADING THE ARRIVAL INTO THE FMS.

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WE WERE ON THE BRAYMER 3 ARR GOING INTO MCI. THE STAR WAS MANUALLY LOADED INTO THE FMS AS IT WAS NOT IN THE DATABASE. BOTH THE FO AND MYSELF FAILED TO ENTER THE TURN TO A HDG OF 190 DEGS. JUST PRIOR TO EXECUTION OF THE TURN AT INTXN BYGEC; WE RECEIVED A CAS MESSAGE. THE FO PROCEEDED TO LOOK UP THE ABNORMALITY IN THE QRH. I BEGAN TO FOCUS ON HIS READING OF THE CHKLIST WHEN AT THIS TIME THE ACFT (ON AUTOPLT) MADE A TURN TO A HDG OF 250 DEGS. HAD THE HDG BEEN PROGRAMMED IN PROPERLY; THE ACFT SHOULD HAVE TURNED TO A HDG OF 190 DEGS. ATC QUERIED US AND AN IMMEDIATE L TURN WAS MADE TO 150 DEGS. THERE WERE NO CONFLICTS IN THIS INCIDENT. LESSON LEARNED ON FLYING THE ACFT AND NOT FOCUSING ON A CHKLIST THAT THE FO WAS CAPABLE OF HANDLING HIMSELF. THE CAS MSG TOOK MY FOCUS OF FLYING AWAY AT THE WORST POSSIBLE TIME. NEXT TIME WE WILL LOOK AT THE STAR MORE CAREFULLY AND FLY THE ACFT FIRST.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE FMS IN THIS ACFT IS A HONEYWELL; AND WILL NORMALLY ACCEPT AN ARRIVAL SELECTION PRIOR TO SELECTING A RWY. WHY IT WOULD NOT DO SO IN THIS INSTANCE REMAINS UNKNOWN.