I am replacing the o2 sensors (butt type.) They branded USOS-3000 (upstream), and USOS-4000 (downstream.) The downstream sensor went in no problem. The problem is with the upstream sensor. The connector on the vehicle has 4 wires. The new part has only 3. Should I join two of the wires together coming from the vehicle, then connect to one wire from the new part? I am fairly certain I have ordered the correct parts. Which wires go where? I am extremely grateful for any and all help! Thanks.