I have a Williams EP5 two a units . 1 powered & 1 dummy w/sound. When I put the dummy unit w/sound on the track without the power unit and blow the horn it works fine. However when I try to run with the power and dummy unit together and blow the horn, I can not shut it off, or the horn blows some times when not activated. The sound works fine but I can't blow the horn. I'm using a Z4000 for power .Any suggestions.