US Spec cars of this period use a single wire for park/stop/indicator lamps (well, two wires, as it is a dual-filament bulb, but the stop and turn signals are combined). So there is no convenient point to tap off separate turn/stop wires. As the cars have an SJB, it is not as easy as just bypassing things, because that does stuff like fast-flash blinkers, throw "bulb out" messages, and can even prevent the car from working (one hacker reported that he couldn't get the car into gear after playing around with some of this stuff). It is not enough to add an amber turn signal, you also need to prevent the stop lights from flashing
On top of that, there are reports of the SJB driver's being damaged by incorrect connections, meaning a new SJB being required, not a path I want to go down.
It *may* be possible to use one of those 2 wire to 3 wire converters, but I would rather find someone that has successfully done this mod, rather than experimenting (I have 14 days to get this fixed otherwise I need to pay for a full new inspection). This model Mustang was never sold in Australia, and up until very recently any 2008 being imported from the US would have to be converted to RHD, so were all professionally done...
Cheers,
Chris.