1) Remove the coupler assembly from each end of the model.
2) Remove the 4 screws from the underside of the chassis. These hold the body in place.
3) Gently lift the body from the chassis.
4) Plug the decoder in to the 8 pin socket and place each speaker.
5) Each speaker has features which locate it in place. The inboard end of each speaker is a firm fit against the motherboard. This is done to provide clearance to the lighting PCB in the roof area.
6) Refit the shell - noting clearance between the body mounting posts and the speaker.
7) Refit the body screws and couplers.