You also said you didn't have a scanner. I highly recommend you drop $20 and get one. It's a critical tool to have if you are going to drive shitty old trucks like ours.
I've never heard of or experienced a bad wiring harness on mine so I can't help you there other than suggest that you might have more than one problem. Or maybe you don't and you need to clean more grounds. Either way it will be a hell of a lot easier to diagnose if you have a scanner. Unless you like going to Vato Zone every other day.
Also, dirty grounds do not equate to a bad harness. Wiring harnesses don't just go bad unless they've been hacked into or modified or damaged in some way. Unless your car was in a wreck, owned by a moron, or has severe corrosion issues I would rule out a bad harness.
The best way to check your cats is to take an IR temperature scanner and see what the temp rise is across the cat after it's been running a while. Consult Google for more details but temp should be hotter on the outlet, I believe.
Since you balked at buying a $20 scanner, I am guessing you don't want a $500 IR. Your other option is to remove and inspect them. If they are bad you'll see obvious melting or the core will be loose, or turning to dust or rattling around. If it still looks like a new cat inside, chances are it's not bad.
The cracks in my manifold were so small I could barely see them at first, and the sound wasn't that loud. However, leaking manifolds will lead to your cats going bad and O2 sensor CEL lights. This is a very common problem on the earlier models.
2000 Frontier XE CC (4x4 parts lift, Eaton rear locker, 4x4 parts skid plate, BFG KO2s, Calmini sliders and bumper, Warn winch, Warn hubs, DT headers & full exh., lots of scratches and dents)
2011 Honda CRZ (stock)
2013 Ducati Hyperstrada (stock)
Last edited by beef tits; 01-12-2017 at 12:37 PM.