there is space for a speaker provided in the fuel tank, replace stock motor decoder with a sound decoder via 8 pin socket,  brand choice is up to you,  soundtraxx and QSI, both have a DDA40X sound sets for their decoders, for other brands, use a GP/SD40 sound decoder.

they are turnout control switches,
the three pin plug on each switch connects to the green wire plug coming from each turnout.
the two pin plugs serve two purposes, one, you can daisy chain the switches together by plugging them together side by side to form a strip of switches, and secondly, the red two pin plug/wire is plugged into the first switch, connecting the switches to the power supply.

1985 MSRP for this set was $75, with a street price at the big name toy stores of about $59, I remember seeing them at K-B on after xmas closeout for $39.
With a VERY few exceptions the is no plastic train set collectors market, with those exceptions being things like Coke and John Deere, and those are not collected by train collectors, but coke and deere collectors.
If you had this set mint and complete, still sealed, it might, and this is a BIG MIGHT, bring the full original MSRP of $75 and up to $100, and most of that would be the "Cool" factor.
An opened used set, even if it's in perfect condition, nothing missing or broken, no scratches,nicks or paint rubs, no creases, marks or extra folds on the mat, would best case, be  in the $35 range, I know of at least one set that a train show vendor has and it is priced at $45, and he has it for at least a year or more with no takers at that price.
My advice, set it up and play with it, enjoy it with the kids.

How to install
http://www.bachmanntrains.com/home-usa/board/index.php/topic,7064.0.html

bump

I don't have a GN1000 handy, but assuming it's the same size as the stock Genesis
board, it will fit in ether loco mounted with foam tape on top of the motor.
It's a close fit on the width, so make sure none of the board terminals or components touch the chassis sides.  I would line the inside walls of the chassis with electrical tape in the area that the board is seated
In the A unit, you can fit either a 16mm x 35mm oval speaker with enclosure, or a 28mm round speaker with enclosure modified for height clearance. Also you will need to remove the factory boards mounting lugs from the rear of the chassis for speaker placement.
In the B unit, installation would be the same, except there is room for an additional
speaker of either size at the front of the chassis.

layout
https://secure.atlasrr.com/mmMOD1/Images/10027.jpg
Atlas DCC wiring diagram
http://www.atlasrr.com/DCC/Layouts/DCC_Wiring_HO-27.pdf

Don't overlook the little 0-6-0 tank either, it's a great little loco for brachline duty haulin' the local.

Walthers sell pads for their cars as a seperate item, for around five bucks, can be ordered direct or thru your LHS
http://www.walthers.com/exec/productinfo/933-1066

For me it depends on the loco, it's assignment in the fleet, my current budget, and what I have in stock or overstocked on.
Fleet daily drivers and club layout locos generally keep their factory decoders and just some have sound added.
My flagship locos generally get premium all in one aftermarket sound decoders, and I recycle the original decoder to convert another loco for fleet service.
My customers choices, however, run the full spectrum, for them I have installed $120 decoders in $20 locos, and $20 decoders in $1000 locos, whatever they wanted are happy with.
Ultimately, the decision is up to you.

Worst case for you Burlington, you could get one of the ATSF northern can motor drives, and fit the Q shell to it.

Quote from: ACY on May 01, 2011, 12:09:16 PM

QuoteThe A unit is a tougher fit, but again the sounder and 15mm would work with the speaker/enclosure mounted in front of the motor under the factory board while clearing the driveshaft.

I don't know about that, have you actually performed this installation, if so do you have pictures. But even if you can, your speaker is still so small that your sound quality in the lower ranges would be very poor at best.

I posted the wrong size, the speaker that fits in the A unit is the 18mm round with enclosure MRC#1519. The clear opening under the board is 19mm W x 25mm L x 12mm D.
The speaker/enclosure is 18mm x 10mm.  Have I done this exact install, no, I replaced the factory decoder with much smaller all in one  sound decoder, allowing use of a 28mm speaker, but I do have a Bachmann FT A  here in front of me to measure and test fit the components into.
Since the OP asked about adding sound to their DCC equipped locos, I suggested an add on sound option as asked for, several methods for installation, and suggested adding sound to the B only without resorting to such drastic measures as gutting a powered loco.
If the OP wants still another better option than gutting his loco, pickups can be added to a metal wheeled boxcar in around five minutes for around 50 cents, and a soundboard with any size speaker they wanted installed as a one evening project.

The MRC sounder with a 15mm round speaker is an easy fit in the B unit, the 28mm would fit with a little creative "adjustments" to factory decoder mounting location.
(remove mounting screws and studs, and remount board all the way foreward using foam tape to open space in the rear.
Since the A and B units generall run as a set, sound in the Bs only works out well
The A unit is a tougher fit, but again the sounder and 15mm would work with the speaker/enclosure mounted in front of the motor under the factory board while clearing the driveshaft.
Another option would be to remove the factory decoder, and replace it with a full sound motor decoder, which would be much smaller than the factory board, allowing more room for a bigger speaker.

The smoke unit is available in Bachmann's online parts catalog,
http://estore.bachmanntrains.com/index.php?main_page=index&cPath=66_68_91
click above
The Niagara parts page (current version)
http://estore.bachmanntrains.com/index.php?main_page=index&cPath=66_68_216
They do not show the lamp, but it is a standard 12 volt with bare leads, and is one that the service dept or your LHS could help you with.

one is a Baldwin 4-4-0, and the other is a Richmond 4-4-0
The unlettered versions normally contain all the detail parts for all versions of that model.
If you look at the southern version of each type, the light, smokebox door, and bell are different.
The unlettered version just didn't have all it's add on parts installed.
Catalog photos are generally shot by an outside agency, who's photographer wouldn't know the difference between a 0-6-0 and a DDA40X.
I have seen many messed up catalog photos, including one from a MAJOR manf. with the locomotives tender turned around backwards on the cover shots.