A320
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 150; Flight Crew Total 10000; Flight Crew Type 6000
Confusion; Troubleshooting
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural Published Material / Policy
General Maintenance Action
Aircraft; Human Factors
I did the walk-around prior to our flight. The navigation light switch was in the # 2 position which I've always known to illuminate the aft (outboard) Nav lights on the wing tips.  The right wing tip was illuminated correctly but the left wing tip light was illuminated in the # 1 position (forward and inboard).  When we switched it to the # 1 position then it illuminated the aft and outboard bulb. This seemed backwards from normal so we wrote up the discrepancy and after an hour of research maintenance said it was normal.  We both explained that we had never seen it before but they said that was how it was supposed to work according to their wiring diagram. So either we are being taught incorrectly and our FM is vague or the maintenance document is incorrect.  But I have never seen two different bulbs illuminated on opposite wing tips with a given switch position.
Reporter stated he saw the same A320 a week later and the same NAV light discrepancy still existed. He still suspects that having two different bulbs illuminated on opposite wing tips with a given switch position is not correct. Because if that opposite light bulb configuration is actually correct; that means all the other A320 aircraft are incorrect; which doesn't seem likely.
During a pre-departure walk-around; a First Officer (FO) notices two different light bulbs would illuminate on opposite wing tips when the A320 Navigation light switch was moved to either the # 1 or # 2 position. When in position #2; the right wing tip outboard aft Nav light was illuminated correctly; but on the left wing the inboard forward bulb was illuminated.