The heater element of the O2 draws an ton of current and voltage compared to the O2 sensor end of it. You don't want the heater ever finding a ground thur the sensor input Grumpy > > > > -- One of those wires goes to the Ho2s [ Heater ] One of the ground > > > wires is redundent. > > Len > Then why did they put 2 ground wires in? > Squash