https://estore.bachmanntrains.com/index.php?main_page=product_info&cPath=69_671_669&products_id=4094 is the chassis I purchased for
reference to replace one on a 90037 locomotive, for reference.

I am a novice at hobby trains, but electrically knowledgable. This is the hookup on a bare chassis purchased as a replacement from
Bachmann a couple of months ago, which was sold with zero documentation of the PCB provided (or even installation information of same
with the chassis). The 4 cables were the only wiring on the new chassis, and I connected them up by following video on the first comment on this thread. There is no old generation parts on this - it was hooked up to test the new chassis prior to putting the old cab on top
of the replacement chassis. The only part moved over is the weight from the old chassis.

I need to call Bachmann directly I suspose and see if I can get any additional information. I am not seeing anything on their website
that documents this board.

To get back to the question - I still don't have thw two wires hooked up for the smoker on the original cab. I suspect that this should be connected to the left SMK+ connector, likely with the red wire to the right. I was rather surprised that there wasn't at least a sheet
of documentation for that board since it is likely to be used to retrofit older trains.
Also would be nice to know where sort of connector is used on the board, and sources for the wire ends connectors that match (and a likely source for same such as Mouser or Digikey or Newark).

Here is a photo with wires connected. This allowed me to test the new chassis as received from Bachmann without cutting any wires
so I could confirm it was working when received. You cannot view this attachment.

Well I actually was able to use the board after watching the YouTube video at the top of this post and connecting the wiring for the chassis as he did.
No connections for smoke box, but was able to get the chuff sounds working using the tender connection using this method.

Is there any better description/schematic for the G912X-PCB06-A card? Also, I may just be blind but is there a wiring diagram that is specific for the replacement chassis that Bachmann currently ships? I am not new to electronics but new to trains. (Looking at some of the other links on this post - very helpful).