a C reading means an open circuit, a full H reading means a short circuit - checking the new sender a pan of water is a good idea, entirely possible it's defective out of the box - also do a resistance check on your wiring .... OTOH the gauge reading H when you short the lead to ground doesn't have to mean that it's good, you need to put a variable resistance in the line [like a known good sender] to tell that
Bill
