I have just returned to the hobby and I have a number of  H O American locos 
That are not DCC ready
Which Zen decoders do I need to fit
(I am going to use the NCE Power Cab system)
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I'd use the Zen218. It is very versatile.

Apart from the 21 pin connector It is also supplied with a plug-in harness with 8 pin, so just cutting off the 8-pin plug will let you hard wire as well.

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