Radar jumping around



On my navnet3d that is coupled to my PG500 and radar. The radar line will move around and clear the screen and then it has to make a complete rotation to refill. This all started when I hooked up my PG500 so I could do overlay. Any ideas? If not how do I disconnect the PG500 so it will quit doing it.
I forgot to add that I constantly have a message that the heading sensor has changed or sometimes says not recieved. It is in red across the top of the screen