Well, if the aircraft includes a night texture (any texture ending with _L) then you need to put it in there and "turn it down" so to speak.  Darken it a bit, and turn down the contrast.  That will blend it into the surrounding fuselage some more.  All the night textures (anything with the _L) will need to be edited if you have changed the main texture somehow.

If this doesn't make sense, or you can't make it work, try posting a shot of the problem (include the name of the aircraft, where you got it and who made it!) so we can get a better idea of what's going on.

Looks like the _L file is missing the correct Alpha Channel.

"Since I dpnt understand the L files al that well."
Most of us  are in this category 
One can learn much by viewing existing work including night Alpha Channels.

Perhaps it's as simple as copying a good set of Extended files/with Alpha from a similar model. Here's a sample:



N.B. Check out the Alpha Channel Where the Alpha is dark the model will render it light (Black=White).