Don't know about the wiring for the wired tethers as I have always been upgrading the sound and didn't retain the old tether.
The IR link is serial data, and it's somewhat likely that you may need to add a buffer to power the locomotive IR LED. The load on the serial data sometimes causes the Cruise Commander to have problems.
The serial data is on pin-24 of the R4LC socket. Oddly, I recently had occasion to break out this diagram again and wire a serial data buffer for the very task you are contemplating. The buffered serial data goes to the + lead of the drawbar IR LED, the negative lead of the LED goes to frame ground. This buffer prevents loading of the serial data and any issues with the Cruise Commander.
