There is just a small piece of rubber insulation between the black housing of the ECM connectors and the "wire management" box (a little piece of plastic with a whole bunch of wholes for each of the wires running to the connector housing). Once you are looking at the back of the ECM connector with the wire cover off, you'll see the insulation/rubber in all the unused wholes. I assume it's probably just there to prevent dust and stuff from getting in there. It's no big deal, I just poked it out with my test light. If you don't poke it out, it'll be difficult to get the terminal in (though you will probably still be able to get it in, it'll just be a PITA) so it's recommended that you poke out the insulation first.