Can anyone tell me the right way to wire up the aftermarket head unit in a 2008 bf falcon?

I need to keep the stock head unit connected for air con etc so how will I get power for the new head unit?

No need to worry about speakers as they are all connected to an external amp. So I believe I need power current, power turn on, remote, aerial, ground etc.

If you take out your stock unit and get a plugin from repco/autopro for bf falcon to Sony or Kenwood or pioneer etc. Will your aircon etc. Not work? Why won't it work? You want to put another stereo in and have the stock unit still plugged in? Anyway to answer your question you'll need to hookup

a power cable with a fusable link (you can buy fusable links from car shop or any electronic shop for cheap) to battery thru firewall via rubber grommet etc. remembering to disconnect battery first of course, but make sure you have stock stereo security code before disconnection

An accessory wire to cigarette lighter or ignition

A ground wire earth to body or steel frame behind dash

And an electric ariel remote wire if applicable

Not forgetting you will still need your amp remote wire and RCA outputs for your amp(s) as you say you won't need speaker wires due to using an amp

I'm still baffled as to why the aircon etc will not work without the stock system plugged in? Or without another system in its place plugged into the same loom to complete circuit.