We start with two identical necklaces, these two I purchased from Forever 21 for under $10 for each.
Because I want the harness to be all chain I'm going to get rid of the ribbon on the necklace and replace it with the longest chain on the dangling part of the necklace by bringing it up on each necklace.
Next I am going to cut off the ribbon from each necklace.
Now our necklaces should look like this, with no ribbon. Take ONE of your necklaces, find the main connector piece (pictured above with red arrow) and gently pull it apart at the seam with your pliers to make an opening in the chain. Once there is an opening, we are going to take our second necklace and link it's connector piece to the connector piece of our first necklace and then use the pliers to put the seam back together so there is no opening.
After connecting your two necklaces it should look like this and you are finished! You may wear it like a vest with the opening in front or in back of your body, or you may connect the connector pieces on the other side of your necklace for more of a harness.
To try this yourself, find a necklace that is long and multi-layered like this one from forever 21, order 2 and get re-arranging!