San Diego 4 connects to Otay Mesa?
Yes. It picks up the end of the San Diego barrier, as it heads up Otay Mountain, East of the Otay Mesa Port of Entry (East San Diego).
It will fill the gap between the new San Diego Barrier, and the next run of bollards, further inland - forming a continuous barrier, continuous patrol road connectivity, and allow a continuous alarm/sensor tripwire for detection - no gap will remain within walking distance of Tijuana.
This will be all new miles, which I don't think the Left wingnuts have yet included into their mantra of "only three new miles of fence have been built" (around Fronton, Texas).
End of the old San Diego Barrier (an easy stroll from a Tijuana neighborhood):
End of the new San Diego Barrier, where San Diego 4 Project picks up: