Hello. I have been trying to uninstall this O2 Sim installed by the previous owner. Can’t seem to find the wiring diagram, plus seems to be a terrible quality installation. So how do I uninstall it? Thanks

 

What a mess. At that point you might as well get another harness and swap that in.

 

This diagram, found in this thread, is for a similar 5-wire o2 simulator.
What it shows is that you tap the following wires: (I found the color codes in the S2000 electrical manual)
RPM signal (blue wire)
TPS (red/black wire
+12v (yellow/black)
ground (brown/yellow)
You can see three taps in your picture (red blocks). The ground tap may be out of the picture,
or he may have used another ground location.
Then the instructions call for cutting the secondary o2 sensor wire (white/red, erroneously listed as red/white on
the diagram), connecting one from the simulator, and taping off the end that goes to the actual o2 sensor.
This white/red wire is the only one you need to splice back to its original configuration - the other wires leading to
the simulator can just be clipped off at the tap, leaving the tap in place, making sure there are no bare wires exposed.
Most taps of this type don't sever the tapped wire, only the insulation, so theoretically you can open the tap and remove
it if you like (putting electrical tape around the cut insulation).
HTH

 

Oh my god...

 

It's really not as bad as it looks - most of those visible splices are in the wires added to connect the simulator. Only
one OEM wire likely was cut, the others were tapped probably without substantial harm to them.
The biggest concern would be that the simulator was likely added so they could remove the cat, and it's not clear
if it's been replaced.

 

Thanks for reminding me why I hate electrical problems.

 

What an unbelievable amateur job! And unsafe, too! Why do ppl insist on doing such things to perfectly good cars? Should be a crime.

Hope you get that trash out of the car, successfully.