Do I connect both white wires together and tie to lighting?

Yes, the gauge is lit using both white wires. The white wire that is next to the red and black wire lights up the pointer (gauge needle). The white wire that comes out of the black box (inverter) lights up the gauge dial (gauge background- numbers etc.). Combine both white wires together and connect to your 12volt dash lighting source to turn on all lights for the gauge at the same time. Connect both black wires together and tie to a good ground point.