Aftermarket VDO fuel gauge help needed Options

[tornik550]

I am trying to use a aftermarket VDO fuel gauge. I am not very clear of how to wire it. Obviously positive goes to switched positive, neg to ground however I wasn’t sure where to connect the sender post on the back of the gauge? I tried hooking it up to the “G” post of the gas tank sender- gauge then reads 0 (even though tank is full). I tried hooking it up to the “WK” post on the gas tank sender and the level goes up to 3/4- even though tank is full. I have used an old gas sender and a brand new one and the same thing happens with both.