I've put a Umelec ATL-2064 Sound Decoder in mine. The decoder is behind the wood load and the speaker in the cab roof, with the wiring running under the cab floor.
It can be seen in 'On30 Tracks'
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by clicking 'How To's', selecting 'November 2004' from the drop-down, and clicking on the 'Producing Real Rust!' link. This lokey also has had a motorized Gypsy Winch fitted, operated by a DCC function.
Regardless of what type of decoder is fitted, it's necessary to remove the water-tank to access the motor so that it can be isolated, but this is not a huge task.
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