Trying to make a texture fill an entire Plane

I know this has come up before, but the other questions and answers don't seem to be helping me. I have several planes with textures attached to them that look like a "light glow" effect that I am using for lighted windows on some building models, but the textures are always centered in the middle of the plane. I am wondering how to make the glow texture fill the entire plane, because when two planes intersect, they seem to "pop" in and out of view. And seeing as how many of the buildings have windows that are extremely close to eachother, I would rather be able to make the plane the size of the building windows, but as for now, I have to scale the planes much bigger than the windows themselves to get the texture to be the same size as the windows, thus causing them to intersect. Any help/advice will be appreciated!