Q: In the absence of a deacon who should lead the Universal Prayer- the celebrant or lector?
==
A: Never the celebrant. He opens and closes the Universal Prayer, and, in that sense, “leads” it.
But see GIRM 71. The petitions are to be led “by the Deacon or by a cantor, a reader, or one of the lay faithful.” The priest is to have someone else read the intentions. It is the prayer “of the faithful.”