Well nothing would surprise me with builders. I've found that many cannot cope with anything outside their own direct experience. First thing I'd check is that the wires are actually connected to whatever you are connecting the speakers to (i.e. wall plate or whatever). If that looks right then check that the wires are intact by sending some voltage through them to check. I use an old car battery and an auto light globe with wires soldered onto it. Just connect the auto battery + & - terminals to one end of the + & - speaker wires and then attach the light globe to the other end of the speaker wires. Don't attach the + & - terminals to the same wire! If the globe lights up then the wires are OK. You can also buy multimeter testing kits of course. I've had mice chew through in ceiling speaker wire but unlikely all would be damaged.