Identifying a wire 740 SE Dashboard

I'm trying to identify a wire that is behind the dashboard, it comes out of a cluster of wires and the ends have been cut and the plastic has been shaved off the end. Anyway, it has a 5 label on it but don't know where its supposed to be for. The car does have some electrical issues, not so much faults, things like the radio will only turn on if the lights are on and the side lights I don't think come on at all. The wire itself: Just above the 2 white wires it came from there. Can anyone tell me what these wires do?

look sliek the din wires from the original radio. and they been cut to be used on a higher powered amp.

The radio will only work with the lights on? You've got it running off the dash lights feed then.

different feed! somones reallllly arsed the wires up! your gonna have to sort it mate

Its going to take a while I think... but it'll be worth it. Although each of the speakers run from the back of my head unit, there is no amp. Although the previous owner had a SubWoofer in the back of the car, although I don't know why as he was a builder... but anyway. The original amp isn't even in use at the moment.

If the original amp isn't even in use, then the radio has been rewired. Badly. I guess that there are crimp connectors or a terminal block in use....? Wire colours are easy to come by (but I haven't got a haynes handy at the mo...)

Is that 7 core cable ? It looks like towbar socket cable i cant see the red wire though , the other 6 colours are right ! Maybe it wasnt used for the tow socket but for some other purpose ????