Speedo head or sensor?

Energy One
I replaced my speedo head last winter with a Dakota Digital. All was fine until yesterday..... It lights and all "looks" fine bu the correct speed does not register. It displays at most 8 mph no matter how fast I go. Returns to "0" when I slow, it just will not increase to actual speed. Probable sensor or head? Both are new last winter. I also started thinking about a bad ground. Anyone have any experience with his issue?
 
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