Eagle Accunav II help

[GoneFitchin]

I recently bought a used boat which has an Eagle Accunav II autopilot. When I turn the unit on all appears fine but the COG bounces all around and never settles down and I'm not talking a few degrees it will jump 90+ degrees at times every few seconds. I ran a gps module self test and it said the module has passed. Any ideas of what the problem is or ways to diagnose my problem would be appreciated.

 

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