so Iv just acquired a 1987 d250 with a 318 here in California. so unfortunately trying to smog this beast has been well interesting. it has a 318 and was missing the o2 sensor... so I searched everywhere on the truck and with no avail could not find the o2 sensor. looked it up online supposedly its supposed to be on the driver exhaust manifold, but my manifold is blank there no hole nothing. so I decided to check the local pick n pull and found a ramcharger with a proper manifold (had the threaded hole but was plugged) checked the back it said china so it must have been replaced at some point. back to my truck got home and scoured the engine bay for the wire to plug in the o2 sensor but I cant find it any where according to a online repair manual its a black wire but cant find anything close to the plug on the new o2 sensor. is it possible someone previously changed my manifold and eliminated th o2 sensor?

here's where I need some help could someone post a picture of their singlewire o2 sensor plugged in from their truck close to this year any help would be much appreciated thanks in advance