LoL, while working on the column could be a fate worse than death, it shouldn't be necessary, and Stoopkid's advice is probably good. All you need to get at is the harness connector at the base, which, if you did use an Arduino, is surely the obvious place to put it anyway. You may well find that that connector has all you need, fully provisioned to make the conversion. As far as I am aware, North America is the only place where cars still flash their brake lights to blink and, indeed, I seem to recall some amber flashers in the US. Everybody else uses separate amber and exported American cars have to comply. They certainly do here. You can be pretty sure this is accomplished by a simple bit of juggling at the harness connector, which is a one-size-fits-all item.