I have a 2003 Hondacivic LX I bought for my son its his first car, but the catalytic converter was removed and it just has headers and a straight pipe to the back muffler (really crappy hack job). I purchased the catalytic converter (Dorman 673-608 Exhaust Manifold with integrated Catalytic Converter Carb complaint) and 940-325 pipe. so the car doesn't have the up/down stream o2 sensors and I'm trying to find the wiring for it so I can install the cat and o2 sensors. Do you have any pictures / wiring diagrams or the best place to get them.

Thanks...

 

Look for the two separate 4P gray connectors on the engine harness.

 

So I found the upstream cable as you can see, but it wasn't in the place as in the picture you sent. I found it tucked in under the air intake the second cable I still couldn't find it.. I went through all the cabling in and around where I found the first cable also in around the back of the transmission. no look. any suggestions what I can do next..

 

Both harness connectors should be on the same branch of the engine wire harness in the middle. It is possible the vehicle has some different harness put in by the previous owner.