There was a long discussion about this here quite some time ago. You might be able to find it.
I bought a used YZ426 twist setup and installed it. From my perspective, Merriman paved the way. I did everything he did to aquire and install the twist.
In retrospect, I might have been better off not installing the second cable that goes with it. It seems uneccessary, but it looks like it came from the factory.
I was able to position the twist grip so the cables go under the front brake lever, futher protecting the cables from damage in a rollover.
Short together to two wires going to the TORS sensor in thumb throttle housing and you should be all set!
Also, this twist pulls faster than any I can remember. I wished for a while that it didn't open the carb so fast, but I've gotten used to it and have no complaints at this point.