Fitting sound in an Auscision N class can be accomplished in two ways, either re-using the 8 pin plug motherboard or hardwiring a decoder, bypassing the DC board.
The sole advantage of hardwiring is that it enables separation of the marker lights from the headlights, for independent functioning and control.
Using the 8 pin plug (latest method)
First the centre hood section is removed, using the method outlined via the hardwire method below. Next, the speakers are wired to the decoder. Following this, the speakers are located into the centre hood section. The 13x18x10 mm speaker locates under the HEP fan, near the #1 end cab. The 23x18x10 mm speaker locates from the #2 end, sliding on to the internal feature behind the radiator inlets. To stop it from rattling some glue is use to affix it in place.
The decoder is then plugged in and the centre cab section refitted. Once tested, the couplers and 6 screws are reapplied to the model.
Hardwiring method (older method)
A 20x40 mm speaker is located at the #1 end of the hood section, under the HEP circular vent. Styrene sheet (or cardboard) is used to provide a sound enclosure around the speaker such that the back of the speaker is airtight and separated from the front of the speaker.
Centre hood removal:
1) Remove the tapping screws from the underside of the chassis, one is located at each corner of the loco.
2) Remove the coupler screws, coupler boxes and couplers. Keep all the bits and pieces in a safe place.
3) Undo the two screws, one either side of the fuel tank and back each one off by about 4mm, or until they are free from the part they screw into. There’s no need to remove them completely from the chassis. These screws hold the centre hood section down onto the chassis and walkways.
4) Next, take a straight-slotted screwdriver, or an X-acto chisel blade. The latter is more effective as it nice and wide, but thin. Place the blade under the walkway, guiding it between the underside of the walkway and the top of the chassis, as shown in the following image.
The purpose of the next step is not to remove the complete body assembly from the chassis, but to invoke enough ‘give’ in the body assembly such that the centre hood section can be lifted away from the cabs and walkways without damage.
5) Gently, lever the body up by a millimetre or so. Work your way along the walkway from right to left and back again, inserting the blade where you can. The underside of the walkway has been superglued to the top of the chassis, and these bonds need to be broken. There are three dabs of glue under each walkway, one above the air reservoir, and one at each end of the walkway near the cabs. One can hear a crack when the bond breaks. The walkway is quite flexible under the force of the blade and will not be damaged if one is careful and methodical. It takes about three or four passes to get the walkway up off the chassis, per side. Do the other side of the model at the same time. The body assembly should sit about 3-4 mm above its original position for the next step.
6) Next, grip the center hood just behind the cab with thumb and index finger and push the cab down with your pointer finger. The cab moves the walkway down, exposing the lower edge of the center hood. Remove the hood carefully, leaving the cabs and walkway on the chassis.
Wiring the lights is the most time consuming part of the decoder installation.
Black -ve: #1 end headlight
Black -ve: #1 end white markers
Black -ve: #2 end headlight
Black -ve: #2 end white markers
Green wire (Aux 1): #2 end red markers (or #1 end ditchlights)
Purple wire (Aux 2): #1 end red markers (or #2 end ditchlights)
Blue wire: Common +ve for all lights
Finally the speaker is placed with two, triangle shaped end baffles made to create a fixed air volume on the back of the speaker. The speaker is fixed into position with CA glue.