So I have made a functional wiring system (inspired by minecraft redstone)
The only problem I have is making so wires that are next to each other get connected just like redstone
I could make these meshes, but how would I can I make it find which one to use?
The blocks are on a 3x3 grid.
The one that is used is dependent only on the 4 adjacent blocks. If there is a wire there, connect it. It is that simple. You only need 4 states for this, not 12. Just rotate them.
Make a dictionary which holds the grid data. Since your game is using a grid, only a single block/part can occupy a cell so you can just make the Vector3 position of the cell the index and the block corresponding to the cell as the value (or a dictionary which will hold the block data in case you have any; just remember to add a Block field which holds the reference to the part).
With that out of the way, when you are placing a redstone, just loop though surrounding cells and check if its a redstone and then adjust your mesh accordingly.
Try the cross products of the unit vectors of each part (the direction from the center to the touching part).
If the cross product is equal to Vector3.up (or negative up), then it should be L shaped.