Cable-building simulations.

So, i've recently wanting to make a 2D top-down game, where you're sopped to build stuff. Houses etc. So, i started to think of some fun stuff that would be nice to have in the game. Heres a list of stuff that i need help with :

1. Cables / power transfer system. So, i want to add electricity to the game. And i want electricity to be transferred inside of cables. And to be able to do that the cables need to be connected. By being placed side by side. And to do that i need the game to detect when the cables are connected/side by side to each other. How would i do that? Maybe raycasting all sides of the cable?

2. Grid building system. I also don't want the player to be able to add example : walls however they want to. I want the player only to be able to place the walls/parts on grids. (maybe 32x32 platforms that they can place parts on, all over the map). How would i do that?

3. Detecting if an object is already placed on the grid. So, i don't want the player to be able to build unlimited amounts of walls on top of each other. Which means that i will need to detect if theres already an object placed where the player is trying to place a new object. How would i do this?

I think thats all i will need to know for now... Thank you for reading.