Thanks - I have continued troubleshooting and it looks like multiple problems after all.
Here are specific situations I have isolated:
One of the displays (RL70RC) "kills" all seatalk communications when it is plugged into the seatalk network.
Autopilot still indicates "seatalk fail" even when seatalk cable is disconnected from the rear of it. Won't go into autopilot mode from standby.
GPS Receiver is not sending out any data.
The instruments are sending data ok, and the second display (RL70) displays depth and speed from them when the RL70RC is disconnected. The RL70 does display chart data from the RL70RC (sent over hsb), and radar works ok.
Any suggestions as to next steps I can take? This would be a great opportunity (or excuse
) to replace everything but I can't afford it, so need to somehow patch things back together.