Thought I'd add a thought on your topic, I am a new member and I have worked and studied much on the Ten Commandments. I do not claim to be an expert, but; have worked with many who are.
Let's begin in Romans:
Romans 2:13For it is not those who hear the law who are righteous in God's sight, but it is those who obey the law who will be declared righteous. 14(Indeed, when Gentiles, who do not have the law, do by nature things required by the law, they are a law for themselves, even though they do not have the law, 15since they show that the requirements of the law are written on their hearts, their consciences also bearing witness, and their thoughts now accusing, now even defending them.) 16This will take place on the day when God will judge men's secrets through Jesus Christ, as my gospel declares.
Man's conscience. like his physical body, is created by God. It is therefore in its very nature to depend on HIM for being and for operation. The capacity to be and to act in and of oneself is an incommunicable property of the Deity. God alone is the source and sustainer of all life; therefore, it is His constant regenerating power that keeps the conscience alive -- where the Law is written. Conscience (CON-means "with" and science means knowledge) and it can be defined as that divine influence at work in man to restrain him from sin. The evidence of its origin lies in this; it always speaks against sin and for righteousness. Thus it cannot be the product of our own hearts, which in their fallen state are deceitful above all things and desperately wicked. (Jeremiah 17:9)
God uses the conscience to give knowledge of His righteousness to all, so no one can stand before Him on judgment day and plead ignorance. (Romans 1) When one becomes a Christian and consecrates himself conscience and all to Him, the Holy Spirit begins in earnest to perfect you in Christ.
As for where do they fit, first; they are in our heart and in our mind, placed there by God to protect us from doing ourselves harm.
Second, considering the Christian's conscience could be called a creature. It is however a weak creature, in constant combat with superior forces. It is a favorite target of Satan, perhaps because he finds it so easily distracted by the cares of this world and so easily pacified by its pleasures. Even the strongest of saints will surrender if no help comes; that help is, as mentioned earlier Christ and His shed blood. Like a crown prince in the cradle the conscience is helpless to defend itself. Stan would quickly usurp the throne if heaven (Christ) did not take the saint into protection. Christ is lie a 24 hour attorney, He never sleeps. To crush the insurrection God conquers the believers heart and brings His own will into it to govern the conscience. Just as a conquered city some yield eagerly to the new government while others continue to plot its overthrow. Some parts of our old nature refuse to give up without a fight. For this reason, it takes the same power to keep a heart as to win it at first. (Grace by the Holy Spirit)
Allow me a question C.W. Ruth once asked -- Can Satan make a perfect sinner? If so, then why can not Christ who has more power, more authority, more love, not make a man a perfect Christian?
My final thoughts from Wesley:
When I speak of Christian Perfection I dare not lay claim to the pre-Adamic nature, nor do I lay claim to the hope that is yet to come; what I can do is say I live with a clear conscience.
(By the Grace and Righteousness of Christ, we are only as righteous as the blood makes us)
A thinker erects an immense building, a system, a system which embraces the whole of existence and world history etc.and if we contemplate his personal life, we discover to our astonishment this terrible and ludicrous fact, that he himself personally does not live in this immense high-vaulted palace, but in a barn alongside of it, or in a dog kennel, or at the most in a porter’s lodge. If one were to take the liberty of calling his attention to this by a single word, he would be offended. - Daniel Milegore (Theologian)