Stereo cables:
I've done some poking about and think:
100% sure the grey one is the aerial (I've traced the wire).
The ones with plugs on the end are the speakers (Do the cross over as maybe they have woofers and tweeters in them, and the tweeters are the ones joined together?).
The black one is connected to the cigarette lighter and i assume is earth.
The red one, since it attached to the ignition, is the ignition one, so where is the power one?
Close up of the where the cables connect:
Does it matter how coarse the sandpaper is that i get, i just want to fix the two posts on the roof: