I can't recall where I read this, but it referred to the number of colonists acting against the British before the "national" military effort in 1775... many were outraged, but only a handful were involved e.g. the Sons of Liberty, Stamp Act protests, Boston Tea Party, etc. Of course, when it was clear that the Colonial government would unite and support the effort by organizing a government sanctioned Army there was more support... but as you point out still not a majority.
The real turning point were the French and Indian Wars (which was the first real World War) during which the Colonials saw just how badly the British used them, then demanded that they (the Colonists) pay for the war. The colonials were of the opinion that through their citizenship and payment of taxes and blood, they had payed for the war.
From The Treaty of Paris (1763) the revolution was a foregone conclusion, becoming only a matter of when.