Hey guys, the search bar failed me. I can find page after page of testing the 02 sensor itself, but I suspect my wiring harness is the culprit.

1987 22R-E. 02 sensor on the exhaust manifold. Single wire.

Bought the truck and found it had a CE code 21.

Found out it was the 02 sensor.

Found the sensor plug was disconnected. Plug on the harness was cut off. Put a female spade connector on it and hooked it up to the sensor plug.

Code 21 persisted.

So I figured it was a bad sensor and swapped it with a spare I had on another manifold. Same thing. Code 21.

So over the last six months I have been refreshing the truck. Tore out the motor and replaced every sensor, gasket, EGR delete, vac line reroute and delete. Stripped it down to what I wanted and painted it up nice. Remembered the code 21 and ordered a brand new Denso sensor.

Fired the truck up first time post-build and there was that little old code 21. Before I go tearing apart the harness chasing that little wire, is there anything else to look for? Anything I'm forgetting or should do first? Thanks in advance for any and all help guys!

The turd in question...