C80 waypoint does not show up on ST60 MFD

[wjj]

I have a C80, with 2 ST60+ and 2 large MFD displays, and 2 Autopilot displays.

When I "go to" a waypoint, the C80 shows the distance and bearing to the waypoint. But the waypoint does not show up the on the instrument display/autopilot control head, the BTW is blank. Other data to the instrument displays show up, such as heading, speed, depth, etc.

On the autopilot displays, The autopilot does not read the GPS, when I try to set it to steer to a waypoint it says "no data" and beeps.

When checking with a electrical tester, the yellow wire reads a voltage of about 10, but fluctuates up and down slightly.

How do I troubleshoot the problem, to get the navigational data to read on the instrument displays??

Thanks for any help!