Posted on 
Feb 28, 2008 11:22 pm This is a little complicated.
So first, lets start with the two ways of wiring in bridge.
The first way is easy. It's 1+ to 2+. What this is doing inside the amp, is taking each side of the amp, and making them one. While one side of the amp is going more positive (Think of a wave sign. The wave moving up, is the positive movement.) the other is moving negative. (The wave moving down.) It is also referred to as "Push Pull". This is placing the speaker in parallel to the amp.
OK. This second way is a little harder to understand. When wiring bridge with 1+ 1-, to 2+ 2-, you are placing a speaker in series with the amp. How this works, is 1+ goes positive, 1- is going negative, but to the other side of the amp. So, it is no longer going to the the same side that it once did. The same with 2+ and 2-. It's strange to understand without seeing, I know. But trust me, this is how it is working.
The benefit with the second way, is to allow a little more current to move down the line with a heavier ohm load.
The only book I can suggest to help understand how this is working is "The Art of Electronics". I rely heavily on this book. The math equations are tough. Real tough. It deals with Calculus, trig, and algebra. But, don't let that discourage you. The authors are very good about explaining what is going on inside the circuit. It's an old, from the 1970's. But the information is still relevant.