exterior cabin lights...???

Ciao to all,I've made the BPA livery for the PMDG 737 series,All work fine...the only thing is that I get to see the lights in the cabin "on" only if i switch on the "LANDIG LIGHTS" on the overhead pannel...WHY..????I must say that I had to move a window and erase one from both the FUSE.bmp that are in the texture folder of the PMDG 737...PAco