There is a pattern to them.
For example, Purple is a fused permanent Live.
It goes to the Interior light (if fitted) and to the Horn.
Both of these have the switch after the equipment, rather than before it.
So Purple with Black trace, is a 'switched Earth', i.e. it is a live looking for a switch.
But there is no way to confirm just by looking, if the Purple/Black is the for the Horn or the interior light switches.
What I don't understand, perhaps John can help here, is why your indicator stalk has the Black/Brown and it's connected to the Purple/Black.

But he's not got a horn button on the stalk, so why is it there?StillGotMy1stCar wrote: ↑Sun Feb 07, 2021 1:15 pm
No it doesn't, please don't. The Purple/ Black is the earth return from the horn and stays all by itself with the Brown/Black.
Read my previous posts, and check the wiring diagram.
Of course if the wiring diagram is wrong then it will need further investigation.
Regards John