Was looking around under my car today when I noticed this. Is there a reason that only 3 wires are connected and not all of them?

 

It would probably help to mention the reason I was even looking is because I got 2 o2 related codes. First is A/F sensor 1 heater system malfunction (P01135). Second is Secondary Ho2S12 circuit heater malfunction (P0141). I assume the first code has something to do with how the previous owner wired this. The second code is just because there is no second sensor plugged in.

 

Well you found your problem.
The o2 sensor is 4wire setup. 2 grounds and sensor out and heater 12volts.

Connect that wire and maybe it will clear out the first light.
If it was me i would get the right connecter and wire it in better.

 

Or hope it doesnt ever rain again.