[Brett]

Check your wiring for corrosion or a loose connection.
Verify that the correct wires are to the correct connection.
Verify solid ground at the gauge. Try another gauge.

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[marc_nelson]

Thanks Brett! i'm wondering if i should take the ground from the sending unit off the gauge and run it straight to the battery?

 

[Brett]

Both the gauge and sending unit need to be grounded.
The sending unit is a variable resistor and the gauge is a current meter.
I believe there should be one more wire to the gauge.
That should be power for the instrument light for night viewing.