Hello Anthony
I hope you read this.
I have read a post or two and you DO appear to know what you are talking about.
Regarding this post you did .....
" Any plain brown wire is an earth wire which is connected to the chassis of the vehicle. Positive feeds are red for permanent +12v (fused KL.30 on the inside of the fusebox lid), and black for +12v ignition feed (fused KL.15). You may have a grey wire at the lamp which is connected to the door switches. "
The thread was about the reading light thing in a Vauxhall.
I have a traffic gadget on the window that I have to power with the ciggy socket.
I also have a bluetooth thingy about my head.
I have taken the readers light thingy out of the centre of the roof and have seen the wires you mention.
What is stopping me just tapping off the Large Brown (for earth) and one of the others for 12V??.