do not know what you are calling a 3 wire simple hookup. you have one wire with 2 leads in it for input to the echo board and 1 wire for the output of the echo board and it also has 2 wires in it. then you have 2 more wires left over that goes to board ground and to 13.8 volts. so how are you saying 3 wire simple hookup.
not sure just how you are figuring out how to make it work properly. the 2 leads that have 2 wires in it go to the shield of the mic plug board and you remove the audio wire from the little board on the mic plug and solder one wire for output of the echo and 1 wire for input of the echo board. every way I look at it you have 6 wires to hookup to make the echo board to work.
you have to pull the audio wire from the plug board and hook the input of the echo to it, the place you pulled the original wire from for mic input, then you hook the other wire you pulled loose to the output of the echo board ,the shield wire you can hook all 3 up on the mic plug board.