If South America is involved, you'll need Galapagos, or alternatively Juan Fernández to get settled. Galapagos can probably support more people and lead to more sustained contacts since Juan Fernández would be pretty marginal as well as not as close to the main centers of Andean civilisation.
But from there, how do you get a trans-Pacific trade network established? South America obviously has stuff and almost certainly sent stuff OTL, and with Polynesians in Galapagos, there's no doubt it would send stuff. The main route would either be through the South Seas and to the Indies, or across the North Pacific to Hawaii and then to the Philippines or Japan. But how much could the Polynesians bring with them? Gold and silver from the Andes would obviously interest anyone in Asia who found it, but it would have to go through so many hands, what would be left for the Asians?
Yeah, the potential of that trade route is huge, but the trade would be very, very slow. It would probably make the trans-Atlantic mail routes of the 17th/18th century look like forum posting here in comparison.
Galapagos would almost certainly be settled from Easter Island which had Rongorongo. But was that actually writing or just proto-writing? Either way, it would spread to Galapagos. Maybe it could evolve into true writing in South America from the Chimu or another group, and then from there be retransmitted back and through Polynesia?