Jose Angel , Feb 17, 2013; 05:07 a.m.
As far as I know, bellows units for Nikon cameras doesn`t have AF connections. Nor you need it.
Once you have set the magnification you want (the size you want your subject on the screen), the focus procedure should be performed by moving the whole bellows+camera unit. If you focus by moving the lens, you can have your subject in focus, but also there is a change in the reproduction ratio.
Reversal lenses on belows is an interesting procedure; you have to check them for better performance, or to look for that Nikon chart where they advice about the best position (straigh-reversed), when using bellows, at a given reproduction ratio.
AF on Micro lenses is interesting for fast shooting, or for "normal" reproduction ratios (close-ups, portraits, etc.); once you are in the bellows-tripod-macro illumination paraphernalia, it is way more practical to have a good manual focus sensivity, via focusing rack (if possible).
I think there are third party tubes that alllow some electrical connections, and you can use Nikon teleconverters for that task, too. For sure others will tell you about them.