I got the dry contact working. All sonoff uses the 120v input to a transformer indicated in the picture. From there it gets an 5v output which it use to run the sonoff. I disconnected the wires from the transformer to pcp using a soldering iron, incase you want to back to the original state you just need to solder back the wire.
Now connect the 5v power source to positive and negative terminal as indicated in the picture. Now your relay will connect and disconnect the live terminals. There is no cutting of the board.
