Sounds like the antenna.Is that radio removable? If so, gunk or corrosion onthe connection at the mount would be my first guess. If that's good,trace the wire looking for a dirty, broken or loose connection.
There are three connectors in the antenna coax on your bike. First one is at the bottom of the antenna, second is under the storage box on the left side of the fairing and the last one is under the storage box on the right side where it plugs into the receiver. If these are all good, you might want to give Sierra Electronics a call. They still repair these old radios and are very helpful.
Thanks to all who have replied so far. It gives me something to start on. The green stereo light does come on briefly, it just doesn't stay on. It flickers and that's it. I won't get a chance to work on the bike until after work tomorrow evening.