Just tested these using a tv remote. The front heads work great but the rear head doesn't respond. If there was something wrong with the rear connection, the display would indicate a rear connection error. So, I don't think it's the line. Anyone have any ideas? Could it be a bad photodiode? or is the rear license light interfering with IR sensitivity? I'm also using a Bel vector 995 as the zr4 display. Your guess is as good as mine.