Perhaps just check a schematic in a shop manual for how the other Rockets' tachometers are wired and do the same??
I'd have to think if you buy an aftermarket tach that clamps to a 1" handlebar the instructions will include wiring instructions. My DR650 didn't come with a tach and the vendor (Trail Tech) who supplied the one I bought listed a couple different wiring options. Dead simple.
In the dirt bike realm several vendors offer different mounting methods and brackets, surely street bike vendors do the same.
Measure the distance between your handlebar clamp bolts - maybe those measurements match those of other bikes so you could use brackets designed for them.
That's all I've got for now. I'm going to finish my morning coffee.