Even the early 2.9 trucks didn't have them. I think they were added in 88? Definitely not there in 86.
87 or 88, I lean towards '88. Electronically a lot of 2nd gen was starting to bleed in.
After sampling a huge number of 86-88 Rangers and B2s the answer to this is "It just depends".
California trucks all had the CEL. A lot of non-CA ones from 86 and 87 had it, a lot didn't. Some 88s didn't.
My 87 came with the CEL "not equipped". The slot in the back of the cluster was covered over and you couldn't even put a bulb in. I cut the patch out of the PCB and installed a bulb/holder, and it worked with no other modification, so all the wiring and software are definately there.
My 88 had the slot open and a holder in it, but no bulb. Can't say if it left the factory like that, but that's how it came to me.
The cluster that I replaced that one with was from an 87 and it was the same way.
The biggest pattern that I have noticed is the tach clusters seem to be CEL ready, and the non-tach clusters don't.