Here are the pics of the wires I cut off from the rx8. They’re from the upstream O2 sensor which is the fuel/air ratio sensor. 1 pic is from I cut off the wires from the harness connector to the O2 sensor that go to the car, second one is the harness connector itself. 1red yellow, 1blue yellow, a pink and a purple. I think I can figure it out color wise on how to solder or tape en back together... but what I don’t know is where does the wire that I circled in red how to??? Help please

 

Your biggest problem is that the O2 sensor wire is a shielded wire in the harness. Connecting it properly means reconnecting the shield properly and connecting the wiring in a way that protects the signal from noise and feedback

if it was me.... i would look for another engine harness with the plug still intact and swap out the harness. It is a bit more work... but you at least will end up with something that works properly