A DC9 CREW DEVIATED FROM COURSE AND DSNDED WELL BELOW GS WHEN THE FO'S NAV FREQ SELECTOR HAD NOT PROPERLY ACQUIRED THE RWY ILS.

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HOW THE PROB AROSE: DURING APCH (FO FLYING); WITH THE ARPT IN SIGHT; THE FLT WAS CLRED FOR A VISUAL APCH TO RWY 36R AT ZZZ. THE ACFT AT THAT TIME WAS LEVELING AT 2000 FT MSL AND APCHING THE LOC FROM THE SE. THE 'APCH AUTO' FUNCTION OF THE FLT DIRECTOR SYS HAD BEEN SELECTED ALONG WITH THE ALT HOLD FUNCTION. (NOTE: THE AUTOPLT WAS NOT BEING UTILIZED FOR THE APCH AND IT WAS BEING HAND FLOWN.) ATTN WAS THEN FOCUSED ON THE INDICATION PROVIDED BY THE FLT DIRECTOR SYS. IT WAS AT THAT TIME THAT I NOTICED THAT EVEN THOUGH IT APPEARED WE WERE NOT QUITE ALIGNED WITH THE RWY; THE HSI AND FLT DIRECTOR INDICATOR WERE SHOWING THE ACFT ON GLIDE PATH AND ALIGNED WITH THE LOC (AT THIS POINT IN THE APCH WE WERE ACTUALLY A LITTLE OVER 2 MI FROM WHAT SHOULD HAVE BEEN GS INTERCEPTION). THE CAPT HAD ALSO SELECTED THE ILS FREQ BUT HAD NOT PLACED HIS FLT DIRECTOR SYS ON. WE BEGAN TO DISCUSS WHAT COULD BE CAUSING THE ABNORMAL INDICATIONS ON MY SIDE. IN FOCUSING ON THE ABNORMAL INDICATION ON MY SIDE; WE BOTH LOST TRACK OF THE FACT THAT THE ACFT WAS DRIFTING L OF THE LOC AND BELOW THE INTENDED ALT OF 2000 FT MSL. AT THAT TIME THE CAPT'S INSTS WERE IN FACT INDICATING THESE DEVS. HOW IT WAS DISCOVERED: THE NAV FREQ SELECTOR ON MY SIDE WAS CYCLED TO ANOTHER FREQ THEN BACK AND IMMEDIATELY SHOWED THE LOC DEV. ABOUT THE SAME TIME WE BECAME AWARE OF OUR ACTUAL DEVS TWR QUERIED US ABOUT OUR ALT AND THE FACT THAT WE WERE L OF THE RWY LOC. THE ACFT WAS THEN FLOWN BACK TO THE INTENDED ALT AND VISUALLY FLOWN BACK TO THE EXTENDED RWY CTRLINE. THE APCH CONTINUED TO AN UNEVENTFUL LNDG. AFTER LNDG; THE TWR ASKED FOR A CALL ONCE PARKED AT THE GATE WHICH THE CAPT DID. THEIR CONCERN WAS WHAT HAD CAUSED OUR FLT PATH DEVS AND WHETHER WE'D HAD SOME SORT OF PROB DURING THE APCH. THE CAPT EXPLAINED WHAT WE HAD EXPERIENCED WITH THE NAV SYS. CONTRIBUTING FACTORS: IT HAD BEEN A LONG DUTY DAY; AND THIS WAS THE FIRST FLT (MAINT FERRY) OF THE ACFT OUT OF CHK FROM A CONTRACT MAINT VENDOR. THE INITIAL PHASES OF THE FLT (TKOF; CLB; CRUISE; DSCNT; AND INITIAL APCH) HAD BEEN UNEVENTFUL. SYS CHKS HAD BEEN ACCOMPLISHED AND ALL APPEARED TO BE FUNCTIONING NORMALLY. THE ONLY REMAINING ITEM TO BE CHKED WAS THE FLT DIRECTOR SYS DURING THE FINAL APCH PHASE OF FLT. CORRECTIVE ACTIONS: THESE DEVS SHOULD NOT HAVE OCCURRED DURING A VISUAL APCH IN PERFECT WX WITH AN ACFT AND SYS THAT WERE; EXCEPT FOR THE FLT DIRECTOR SYS ON MY SIDE; FUNCTIONING PERFECTLY. THE CAPT AND I LET OURSELVES BE DISTR BY SOMETHING DURING A CRITICAL PHASE OF FLT WHEN WE SHOULD HAVE JUST IGNORED THE INDICATIONS AND CONTINUED THE APCH TO LNDG USING VISUAL CLUES I SUBSEQUENTLY DID. WHEN BRINGING THESE ACFT OUT OF MAINT WE TEND TO WORRY ABOUT THE RAMIFICATION OF BRINGING AN ACFT TO A HUB STATION WHERE IT WILL BE PUT INTO SVC SHORTLY; AND WHEN WE HAVE PROB; WE TEND TO TRY AND TROUBLESHOOT THE ISSUE IN AN EFFORT TO PROVIDE MAINT FOLKS ON THE GND AS MUCH INFO AS POSSIBLE TO HELP THEM RESOLVE THE PROB(S) IN A TIMELY MANNER. BUT AS WE FOUND OUT; TRYING TO ACCOMPLISH THAT IN THE ARPT ENVIRONMENT; AT NIGHT; AFTER A LONG DAY; IS A MISTAKE. WE WILL NOW DISCUSS WHAT WE WILL AND WILL NOT DO MORE THOROUGHLY DURING THE APCH BRIEFING TO HOPEFULLY PREVENT THIS FROM HAPPENING AGAIN. NOTE: WE MADE A LOGBOOK ENTRY CONCERNING OUR PROB DURING THE APCH. MAINT CHKED THE ILS/LOC SYS ON THE ACFT AND FOUND NO ABNORMALITIES. SUPPLEMENTAL INFO FROM ACN 707948: NIGHT MAINT FERRY. CLRED FOR VISUAL APCH RWY 36R. COPLT FLYING AND CALLED RWY IN SIGHT. I SWITCHED FROM VOR TO ILS AND NOTICED THAT WE WERE WELL BELOW GS BUT ARPT WAS IN SIGHT. COPLT SAID HE HAD ABOUT A 30 DEG LOCK OFF WHEN LOC CAPTURED. WHILE ANALYZING SITUATION AND BEGINNING CLB TO GS ALT; TWR CALLED FOR US TO COMMENCE A CLB; WHICH WE HAD JUST INITIATED.