I have a green wire with white tracer coming from my turn signal harness and cannot find a corresponding wire under the dash. Looking at my schematic I almost thought it went to the stop switch but find no female for my male.
I have a 1/76 and had the same "question" a couple months ago. I found a thread on here somewhere which, I believe, @Coolerman noted it was an abandoned wire carried over from the pre-75 years (don't quote me on that) that Toyota didn't bother changing the wiring for. In other words, it does nothing. Mine was recently re-wired and so far as I know everything is working fine without it hooked up. Unfortunately I can't find the right thread where I first read that.