8-pin vs 9-pin decoder harnesses

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Mark Mathu - 31 Aug 2010 18:54 GMT

A question from someone who is not decoder-savvy:

Why do some HO locomotives come with 8-pin DCC harnesses (for example,
the Atlas SD35) versus some that come with a 9-pin harness (for
example, the Walthers RS-2)? What's the difference in operation of
the plug? How does that limit decoder choices?

Atlas SD35: http://www.atlasrr.com/HOLoco/hosd35c.htm
"... NMRA 8-pin plug for DCC ..."

Walthers RS-2: http://www.walthers.com/exec/productinfo/920-35127
"... factory-installed 9-pin DCC harness…"

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Reinhard Peters - 31 Aug 2010 19:21 GMT

Mark Mathu schrieb am 31.08.2010 19:54:

> A question from someone who is not decoder-savvy:
>
[quoted text clipped - 8 lines]
> Walthers RS-2: http://www.walthers.com/exec/productinfo/920-35127
> "... factory-installed 9-pin DCC harness…"

The 8-pin is more common in Europe while the 9-pin is widely used in the
US. In fact I would have serious problems to get a 9-pin decoder over
here in Germany (except an US decoder imported by a special US model
railroad store).
The 8-pin plug has often only 7 line connected. PA1 and PA2 (green and
brown) are often not or only green (PA1) is connected. The 9-pin plus is
fine to have all lines and usually has all lines connected.

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Mit freundlichen Grüßen
Best regards
Reinhard Peters

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Mark Mathu - 03 Sep 2010 00:18 GMT

>The 8-pin plug has often only 7 line connected. PA1 and PA2 (green and
>brown) are often not or only green (PA1) is connected. The 9-pin plus is
>fine to have all lines and usually has all lines connected.

Can a person use an 8-pin decoder in a 9-pin socket? What are the
results?

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Puckdropper - 03 Sep 2010 17:51 GMT

>>The 8-pin plug has often only 7 line connected. PA1 and PA2 (green and
>>brown) are often not or only green (PA1) is connected. The 9-pin plus
>>is fine to have all lines and usually has all lines connected.
>
> Can a person use an 8-pin decoder in a 9-pin socket? What are the
> results?

The form factors are different, the 8-pin is 2 rows of 4 pins, while the
9-pin is 1 row of 9 (much smaller) pins. The difference is merely
physical, adapters are available to go from one to the other.

Pictures are available here:
http://www.litchfieldstation.com/DCC-University/SelectHarness.htm

Puckdropper

Signature

Never teach your apprentice everything you know.

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Craig Zeni - 07 Sep 2010 02:05 GMT

> >The 8-pin plug has often only 7 line connected. PA1 and PA2 (green and
> >brown) are often not or only green (PA1) is connected. The 9-pin plus is
> >fine to have all lines and usually has all lines connected.
>
> Can a person use an 8-pin decoder in a 9-pin socket? What are the
> results?

Yes, with a 8 to 9 pin adapter harness. In fact I buy 'blank' eight pin
male plugs and solder up my own harness. I use a lot of Train Control
System T1 decoders which are 9 pin but they came with the female plug on
a hardwire harness to be soldered into the model. But I take the eight
pin blanks, color match the harness to the plug and solder it up. Voila
- 9 pin decoder on an eight pin harness. And of course you can buy
those harnesses premade from TCS and others.

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Model Forum / General / Railroads / September 2010

8-pin vs 9-pin decoder harnesses