Aircraft lighting

How do you map out where to place lights on aircraft? Would you get the numbers from FSDS or another way, cant seem to place the lights in the right spot. Thanks for any help you can give.
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I am adding the lights to the config file. FSDS is set to metters at this time. Do I get the coordinates from placing the pointer on the X, Y, Z of the axis and if I have FSDS set to metters will these coordinates also work?
And one more question,
light.0 = 3, -6.60, -19.29, 0.79, fx_navred ,
How do the above coordinates determine where the light is placed, is the first number for going to the back of the plane (aft), the 2ed number for left and right (port & starboard) and the 3rd number for going up and down?