I really don't see a connection between the "power of sin" and the Spirit of Truth.
It's the Spirit of Truth that works inside us to reveal God's perfect requirements that his law demands.
When he speaks to us inside, we realize we can NOT meet those perfect requirements and thus we "fall short". This "gap" is the part of us that is "missing" or "sin". The true meaning of the original word for sin is "missing" (the mark) or "falling short".
(This is a side note, but I am convinced that the "gap" is the same spiritual gap of Luke 16:19-31 in the parable of "Lazarus and the rich man". We are currently separated spiritually from other parts of our spiritual selves. One part of us is "Lazarus" and one part is "the rich man" and a third part is "Abraham". Between them there is an impassible "gap" or "chasm". No man right now can "cross this (spiritual) chasm" as no man can fulfill the law perfectly)
This is the job of his Spirit to reveal this to us so we will ultimately trust in his righteousness as a gift. But first he must reveal to us "the truth" that he law demands (via the spirit of Truth/the helper), it exposes and convicts us of "sin" which is just our inability to perfectly uphold his perfect law.
But I tell you the truth, it is profitable for you that I should go away; for unless I go away the Helper will not come to you; but if I go, I will send Him to you." And He, when He comes, will convict the world concerning sin and righteousness and judgment; John 16:7-8
All God needs to do is reveal his perfect standard to us in our hearts and we KNOW we "fall short" and this reveals sin to us. At this point, we can choose to be condemned inside (which is really US trying to fulfill the law ourselves which is PRIDE) or we can freely accept his righteousness as a gift and thus, he fulfills the law for us and in us.
