I fitted the decoder the same night still suffering from that disease I caught in the afternoon, I think they call it enthusiasm.
Here is a picture of the install, note that I trimmed back the metal chassis projection holding the rear headlight to make room for the speaker and tapped the decoder and wires to it. I installed the speaker on edge held by yellow 'Blu-Tack'? Also the speaker is facing forward and the sound actually sounds like it is coming from the middle to front instead of the rear which is good.
A while back I bought a tiny Full HD video camera fitted with a micro SD memory card and here is a video taken tonight of a run over the main line. The camera is in a K wagon in the train behind the 421. My apologies for the date in the corner, unfortunately there is no way to turn it off, the camera is a bit basic also it doesn't seem to have the clarity that I would have expected of Full HD but I suspect it is the low light conditions and perhaps the lens quality, a common problem with small cameras.
Click on the YouTube logo below to see the video larger and better on the YouTube site.