Start checking around 195˚. Some will hit the "sweet spot" earlier than others. A lot of this is dependent on the age of the animal. In younger animals the collagen will break down sooner and at a lower temperature. In older ones, it's much tougher, requiring much longer and a higher temp to break down. What happens is the connective tissue will suddenly "break", or melt, magically transforming from tough collagen to liquid, lip smackingly good gelatin. The result is a tender, juicy piece of meat. Pull it out too early and the meat will be hard and dry as it hasn't hit that magic "breaking point". Let it stay too long after the break, and it will be soft and dry, as all the juices created by the break will have been allowed to cook out.
The "jiggly, wiggly" brisket is the result of hitting that sweet spot JUST as the connective tissue breaks. It's all still in the meat, but entirely in its liquid form, so your brisket is essentially a sponge.