Nick: Thanks for your link back to 2016. I'm doing a CC"M". upgrade on my 38053 NYC Mohawk and running into this serial data install issue with the serial data "buffer".
I see all you did was run pin 1 from the 10 pin J4 connector over to pin 24 on the R2LC and it worked without a serial data buffer? Did you solder directly to the back of the R2LC?
Regards,
Larry