This is what I had when I removed everything to get ready for the installation. The weight is going to have to go if I want sound and not mount the speaker in the cab. I decided to go for lower weight. Removing the weight reduces the weight about 34%. I'm going to use LEDs to replace the bulbs.
Here's a shot of the bottom of the motor. You can see where the paint has been scraped away just below the hex nut to allow the frame to conduct electricity. I insulated this with tape then reinstalled the motor. The orange lead that comes off the top of the frame in the front where the light bulb mounts will be attached directly to the decoder.
This is the speaker installation. I made a speaker box from 0.040 styrene, installed the speaker with Goo, though I think next time I'll use silicon, and it press fit into the the front of the hood right behind the front LED. The wiring from the LED is behind the speaker.
I used another piece of styrene to attach the red and black wires to keep them away from the wheels. This also shows the decoder itself with all the wires from the decoder soldered to their respective leads and insulated with heat shrink tubing.
Here's another shot of the completed work before closing things up. I tested it extensively before closing it. It's a tight fit. You can see an end of the orange insulating tape from the bottom of the moter where the purple piece meets the frame in this picture. Also, I attached the rear LED to the plastic light tube that runs thru the top of the cab by nipping the end of it off and polishing it so it will transmit the light. I attached the front and rear LEDs with small pieces of black heat shrink tubing.
Lastly I installed the Loksound file for the 6 cylinder Alco. It works well and sounds good. My only criticism of the sound files is that the horn sounds as if it is about a mile away. It may be possible to tinker with that particular sound file and boost the volume using sound editing software. I haven't tried that yet.
That's it. This is my first installation, as I said. I think if I was able to do this, anyone can install a sound decoder in the Proto S1's and S3's.
Mark
Nice Job. I did mine a bit differently. I put the speaker where the fuel tank goes, and it fit perfectly. Even sounds good with no baffle. That allowed me to keep the weight. Mine was done over a year ago, and it's been fine. In fact it's my most popular loco, and gets used all the time. There was another post where I was trying to describe this install, and it seemed like all the other posters were ignoring me, or saying things like the .9 amp micro will burn out. It won't!
I changed my horn sound using the programmer. I thought the one in the stock file sounded like a bus or tram. I also set the sound to operate like a QSI, where it's off, until you "start" the loco by pressing F6 or F8 (configurable).
EDIT finally found link to original page with motor isolation photos.
http://rides.webshots.com/photo/1163959369053026236wSyPmw
Might be of help to others.