soooo..... (this is thinking back a while.....)
On the (square? or maybe round) plug that joined the satnav to the stereo I poked around and tested all combination of the plugs (used a paper clip). I found two, that when join, would power the unit on. Stripped back those wires and connected them to a relay base like this (https://www.jaycar.co.nz/horn-relay-base/p/SY4069) with this relay (https://www.jaycar.co.nz/spdt-30a-horn-relay-12v/p/SY4046). In my earlier post i think i got the pins on the relay around the wrong way... Have a read up on how a relay works - it will help.
So, in terms of wiring the unit I made use of vampire clips and chocolate blocks soldering would be best, but this has survived nearly 3 years with no issues
85 goes to ground, typically black wire in your radio harness, use a multi-meter to check and tap it in with a vampire clip
86 goes to the switched 12v source (the one that turns your radio on) usually red or yellow/red, again a vampire clip
Its always good to test thing as you go, so in this case turn the car on (so the radio turns on) and using the continuity function on your multi-meter check that pins 30/87 are connected.
Then, using the chocolate blocks, connect the stripped wires to 30 and 87. Some relays may have 5 pins, thats fine, you don't need the last one.
It may sound hard, but really its not. I'm no electrician, i've played around, blew a few fuses, wrecked a few bulbs/voltage regs ect, if in doubt, use your multi meter. If you get nothing, its likely you blew a fuse - nothing major, that's why you have fuses (also grab a few spares - i think the radio circuit is a 10a... may be wrong on that....)
If that all works, you will now have a working after market stereo and a/c controls!