I bought an ARB-704 for my Yaesu FT-991A and Amplifier Ameritron AL-80B. It has the interface cable PNP-8M. The light of the ARB (XMT light) is always on even I did not plug power into the ARB-704. It seems there is a locking PTT button or menu option on the radio that is holding the radio keyed. Any thoughts about what's wrong or what do I need to do to setup the radio menu? Thanks.