To all the model railroaders that purchased a Bowser ALCO C636, this is for you.
This was expected to be a relatively simple changeover but it didn't take long to realize, what a can of worms!! This locomotive originally came with a v4 Select decoder and wanting to put a v5 decoder into it the fun began.
There are several different sound files for the ALCO 636 engine downloadable from the ESU website. Everyone of them has different physical AUX mappings to the various lights that come with the respective locomotives. It was the ditch lights that would turn out to be the hair puller. The author contacted Bowser and through the very helpful Lee English he was told the correct sound file was 94469 but he was not entirely sure of the correct AUX mappings. He supplied the author with the electrical diagram of the engine shown in figure 1.
Fig.1 Bowser C626 Electrical Diagram
Along with this was the motherboard plug layout diagram shown in figure 2 which would prove to be a great aid in figuring out all of this.
Fig. 2 Motherboard plug diagram
Before changing the decoder, testing showed that everything worked as advertised. The ditch lights worked as did everything else. Of course, as soon as the decoder was changed to a v5 the ditch lights refused to function.
The author and Mark Granville of the groups.io LokSound forum poured over these diagrams and after the author did some wire tracing inside the shell both decided to try AUX 5 and 6 as a best guess, no joy. Looking at this diagram the author noticed that AUX2 is only shown as an input to the 21 pin plug and it is no where else. So, he (why not?) mapped AUX2 to the front ditch light. VOILA!! it worked.
Now for the rear ditch light. Taking a look at the wiring coming from the rear LED board one of the wires went all the way to the X1 plug which, in the diagram, points to AUX4. The author took a look at the back of the locomotive and printed on the rear LED board was "AUX4". Hmmm... 'nuff said. AUX 4 worked. Problem solved.
Lessons Learned
First, even though you may have the diagrams of an entity you are trying to decipher, last minute changes, and not necessarily last minute ones, do not always make it to the diagrams that are released. That is what the author and Mark believe happened here. Keeping documentation in sync with changes is at best a difficult task and often not done.
Second, visually inspect whatever it is you are working on (and don't just give it a once over). It may save you time and frustration (AUX4 anyone?).
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