Fig 2: There is room in the rear of the chassis for a 1” diameter speaker with enclosure. You will also need to remove the existing PC board.

Fig 4: Trim the front truck wire that was attached at the back of the board. Install the Soundtraxx board per the diagram supplied with it. Solder the connections and put the clips back on for insulation (they don’t hold well enough to the Soundtraxx board to use them without soldering).

Fig 5: This shows the final installation. The 1” speaker and enclosure is held to the chassis with double-sided foam tape (I used 2 layers to clear the truck). The decoder is held in with DAP BlueStik (there are many brands and colors of the same putty available in craft stores). It sticks to most everything, but comes off clean and doesn’t leave a residue. I also used a voltage regulator with resistors to set the headlight to about 2 volts so the bulb was bright enough. You could also use an LED with resistor or a low current 12v bulb. Be careful with the 12v bulb as it creates much more heat than the 1.5v and can melt or distort the mounting plate or the shell.