i bought this truck needing a valve job--most was already disassembled --almost done putting this puzzle together-my only problem is o2 wiring into the harness-all were unplugged when i got it--I know which o2 sensors are un stream etc--but the body harness connectors are not marked and all are long enough to reach all o2 sensor plugs--how do I tell which plug goes to which sensor from the harness?