Yes, that would do it. Good job noticing it was backwards. That is a FET (field effect transistor) which is responsible for momentarily muting the audio signal while the relay is switching to keep the relay click out of audio path. Since it’s backwards it might be constantly keeping the signal muted, so that’s why everything is really quiet.
Email us at info “at” zeppelindesignlabs.com and we’ll explain how to get a new FET.
-Brach