[Redog]

GM loves using black wire for ground. Throws me for a loop everytime I replace a switch or outlet in my house, because in that case, black is "hot"

Are you sure it's not working? Is there ice, frost or dew on the back window? You are not going to feel the grid getting hot. Rear window defrosters don't work that way. You could turn it on and see how much your voltage drops on the entire car. Rear window defroster uses a lot of power

The "other" connection is for the radio antenna. It looks like an RCA jack

If all else fails, then yes the mod is probably bad