Your best bet is a steering wheel control adapter - Connect2 and Metra do them, and as well as providing steering wheel controls (for most headunits - check to make sure that yours supports them) they also provide signals FROM the CAN networks for things like reverse, handbrake on, 12v sense etc etc. Even if you don't want to use the steering wheel controls then this is the best way to get a reverse signal.
It'll save you running a long wire back from the tail lights!!
The pic show one of the Connects2 units I've used with Alpine gear - the short wire in the top left corner is wher it hooks into the headunit. the rest of the connections are via the Quadlock, with wores breaking out for reverse, handbrake, etc etc
This one is a STK279 with the Alpine pigtail
It'll save you running a long wire back from the tail lights!!
The pic show one of the Connects2 units I've used with Alpine gear - the short wire in the top left corner is wher it hooks into the headunit. the rest of the connections are via the Quadlock, with wores breaking out for reverse, handbrake, etc etc
This one is a STK279 with the Alpine pigtail