gas gauge wires

I've searched and searched and haven't been able to find the answer on my 99 there used to be a 4 wire plug that goes into the back of the gas gauge the previous owner change the gas gauge and wired it backwards. the gas gauge that he put in there is a 3 post gas gauge if anybody can help me find out where are the four wires go to that would be a great help I know for sure that the black wire ground, the white wire is for the light but I don't know what the other two wires go to or which post to put them on.

From the sending unit? It is a resistive device so it doesn't matter with those two wires.

Not from the sending unit from the og wire harness. I know the black needs to be grounded the white is for the gauge lights (where do I need to place this one) what do I do with the other two as well. With out the white wire plugged in the gauge lights don't work and the ground wire none of the gauges work. I can direct wire the gas gauge this I know, what do I do with the harness wires.