i find it interesting, in the US service manual wiring diagram, it lists turn signals but there are no paths shown. if you turn to the section 12 (electrical system) it shows the wire connections for the turn light switch (for the EU) orange +, Gray -, for one side and Sky Blue + and Gray - for the other side. I'm wondering how far back has anyone traced the colors. I haven't looked yet but I suspect they are in the trailer wiring harness. It might be a better place to pull from. I'll let you know what I find.