how do i put lites in windows of a house cake?

I wouldn't put LED lights directly onto a cake. The wires do get hot, and the wires usually contain lead so they're not food-safe.

I did a car cake that had headlights that lit up, but I used small lightbulbs that light up when you twist the bases. I stuck them into the cake when I was setting it up, and they stay lit for up to 8 hours or something like that. This is what I used: <a target="_blank" href="http://www.amazon.com/s/?_encoding=UTF8&camp=1789&creative=390957&linkCode=ur2&pageMinusResults=1&suo=1355685922639&tag=acatoreva-20&url=search-alias%3Daps#/ref=nb_sb_noss_1?url=search-alias%3Daps&field-keywords=led%20mini%20party%20lights&sprefix=led+mini+party+l%2Caps&rh=i%3Aaps%2Ck%3Aled%20mini%20party%20lights">mini party lights</a><img src="https://www.assoc-amazon.com/e/ir?t=acatoreva-20&l=ur2&o=1" width="1" height="1" border="0" alt="" style="border:none !important; margin:0px !important;" />

Use google.

http://www.cakeb0t.com/tutorials/cakeb0t-cake-tech-how-to-use-lights-in-your-cakes/

Your string would be OK inside a gingerbread or cookie or dry gumpaste house on top of the cake proper, because you will need some space for a battery pack. Put the house onto a base of the same cookie, then that sits on double-foil-wrapped cardboard base to insulate it from the cake's icing.

Think about how the wires are run in a real house (or at least, how they were run after knob-and-tube was outlawed, and before Romex was invented):

The wires are run through conduits. Tubes that provide either an extra layer of insulation, or a grounded metal enclosure that will, if the insulation on the wires fails, instantly blow a fuse with a short circuit, before anything worse (like a fire, an electrical burn, an electrocution) happens.

In practical terms, if you need to pass non-food-safe wiring through a cake, you need to find some sort of food-safe tubing that's big enough to pass your wiring through, and then figure out a way to embed that in your cake.

I'm not entirely sure (and I don't think I'm alone here) what you mean by a "house cake."