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Hella driving lamps mounted on end of wing struts of CH750. Pictures in my "Can-Zac Spycam" photo album on my profile this site. KISS
The bulb housing has a square tab on the back side in one spot. That is an alignment tab. The landing light housings has a square cutout in the mounting circle to recieve that tab. I forget the location of the alignment cutout. Go to the airport and look at the landing light mount of a certified airplane and you can note the location of the cutout for the tab. I am sorry I cannot give you that info by memory, but I cannot.
The beam of the 4509, by the way, is not a circular spot type beam, it is an oval shaped beam. You should be able to hook the bulb up to a battery and point the beam at a wall and see the oval. You want the wide part of the beam in the horizontal plane so you will have a "fan" of light in front of you. If you install it with the wider "fan" part of the beam vertical, you will not get much light on the ground in front of you, just a knife edge of light.