This is an older router, but I wanted to put a serial connection on it anyway.
I have done it in the past, I think to this one but the prior ones did not have a console soldered on.
Also this one will have the mini din connection.
Hope I got the pins right. Documents may switch the RX and TX, my default is usually white is RX, blue is TX and black is ground.
It is OK to flip RX and TX but wiring ground wrong can kill the router.
I made a bunch of mistakes soldering. Still not feeling well. Maybe I should have waited a bit more till my head cleared.