The Code 3 2100 bars do not synch any of the LED heads. Each LED module has l=a small circuit board on its backside. Off this come 6 wires. They are power (12v DC), ground, 2 small white wires for DIM, and then 2 wires that go to the actual LED head. You'll only really mess with the power, ground, and the DIM if you have it or want to DIM it. Ground should just go right to the lightbar ground, so that's easy. The power wire is usually tied into the power wire from the opposite side's respective LED head, and this wire goes to the controller, which then goes to either Level 1, 2, or 3. When the controller gives 12v to the respective level, 12v goes to the LED module, and it flashes in its set pattern.
On the back of each LED module you'll see the mini circuit board. In about the middle of this board there will be two pins that stick out. They are relatively large, and they stick out a good 1/4", and are about 3/16" apart from each other. They are pretty distinct, nothing else on the board looks like them. Using a flathead screwdriver, just touch the pins together, and it changes to the next flash pattern. In the install guide it will show you what patterns are in which order, but there are something like 9 different patterns, plus a steady burn, and a pattern that cycles through every pattern. Holding a screwdriver to the jumper for 5 seconds reverts to steady burn.
Be advised, the bad thing about the 2100s modules (I have the same modules on my Excalibur), is that every module cycles at a different speed. For example, if you set a red module and its corresponding blue module to flash 3 times fast then pause before flashing again (One of the preset patterns that I'm using), on mine they start together, but the blue flashes slightly faster, so after a minute or two they don't look synched at all. I'm guessing this is because the blue draws slightly less power than the red.