Hi, thanks for the question! We get that one a lot. I'm not sure that installing the light and sound kit during the build makes it any easier to hide the wires-- we have some photos here showing how well the wires are hidden during a post-build install. I think the main issue with installing as you build would be that the light/sound kit instructions aren't written to match the LEGO set build steps, so there would be a lot of back & forth and waiting and then picking up again from where you left off if you were to try it that way. It's definitely possible, we just couldn't provide any specific help on that approach.
Tanner Saadi I haven't been building for long, but everything I've built, I've lit, and I can only do the wiring as I build. I have found my hands are just too big to fit in those small spaces once it's built, and I despise trying to disassemble a section. That prospect works for me how opening a bag of chips worked for my ex, with Legos all over the floor. I find I am really good at being able to hide the wires if I can be at exactly the right build step to see how it all goes together. A really good example of this is the lights on top on the semi that hauls the mixer carnival ride. Immediately behind the large curved pieces that say Mixer are 3 2x4 bricks mounted 3 across. I had to snap the back part of each black piece to the front of each white brick, then route the wires under the front edge of the brick, but behind the curved piece, so I could snap the front of the black piece, the part holding the wires under tension so the bricks would go together without huge cracks, onto the back of the curved part while snapping in the 2x4 brick. The result is there is not a big cluster of wires crowding up the cab, just the 4 individual wires running tightly down the back, which were then twisted into a cable running down the outside of the back of the cab, just like in real life. I would have gotten frustrated trying to reverse engineer it, but that's just me. I would suggest you try installing while you build. You will know VERY quickly if that way will work for you or not, and if it doesn't, you can put the lights aside until the model is finished.