I was trying to install an Ecobee thermostat, and there was no C wire installed. When I went to install the power extender kit, I saw the standard C wire terminal was broken out of the black plastic casing, and I couldn't attach the C wire. There appears to be a secondary C terminal that is a different style with a plastic plug plugged into it, and then the wire is spliced and connected to the wire heading to the AC unit. Can I add a second wire to this plastic plug, is this a secondary C terminal that should work fine? I attached a pic.