Look at Chapter 8 of Adv. Prax.
Adversum Praxaen 8.5
“As for us [...] because “I and the Father, we are one.” [John 10:30] This will be the Truth's (προβολη) emanation, the Guardian [Or: "the Keeper" "the Watchman"] of the unity [Or: "of the one-ness"], by which we declare that the Son is an emanation from the Father, but he is not separated from Him, just as the Paraclete teaches...”
Tertullian hasn't worked out all the kinks in his theory's yet. He vacillates from teaching heretical ideas (like above) that appear more like what he's fighting against (Sabellianistic One-ness) and his doctrine of the Trinity of persons.
But he clearly states that the origin of his ideas, i.e. the
Montantist "Paraclate".
Adversum Praxaen 30.5
“This man in the meantime has become the recipient of the gift that came from the Father, which he poured forth, the Holy Spirit [Or: “the Spirit of Holiness”], the third name of the Divinity, and the third stage [Lit., “the third step”] of the Divine Majesty, the Preacher [Or: “the Publisher”] of a unified [Or: “sole” “single”] monarchy, but also the Interpreter of the economy, for anyone, who will permit admittance to his sermons of THE NEW PROPHECY, even the Leader of all truth [Or : "the Guide of" "the Conductor of" "the Escort of" cf. John 16:13] which consists in the Father, and the Son, and the Holy Spirit, in accordance with [Or: “according to”] the Christian mystery...”
When Tertullian says "deductorem omnis veritatis" he doesn't quote the Bible, he's using a Montantist title, a description
derived from John 16:13 which says in Greek, either εἰς "into" or ἐν "in" all the truth (Jerome reads "in" also), rather than and contrasted to Tetullian's genitive omnis "of" etc.