97 oil press. gauge

I know that the oil pressure gauge is a fake and is in reality just an analog idiot light, but how can it still read normal oil pressure with the sender unit wire disconnected from the sender unit? If the sender unit grounds the wire with normal a oil pressure condition, then a disconnected sender unit will not ground and shouldn't the "gauge" then read zero oil pressure? Mine is totally unaffected by disconnecting the sender wire, still reads the same normal prss. with or with out the sender unit were attached. Thanks, Mike