Owning a few different, both DCC ready, DCC, and DCC with sound Spectrum, and Sound Value locomotives, I've had occasion to add or want to add DCC and / or sound.   Or switch to a different tender type (slightly larger for my Decapod  -  adding a Consolidation tender). 

What would really help would be a set of .PDFs with the engine to tender connections layout for each loco (and variants, such as 2-8-0 with or without DCC and / or sound).  Also including info on headlights and backup lights such as bulb or LED, voltage, size, etc.  The information must be somewhere inside Bachmann, and hopefully the effort to publish it wold't be excessive  -  and a lot of us would really be thankful.))