How to use a 21-pin decoder in a locomotive with an 8-pin socket

Whilst we crunch through a mound of unedited video filmed during June 2018, we thought we’d put out a short tutorial outlining one approach for making a custom 21-pin to 8-pin harness to enable the use of a 21-pin decoder in an 8-pin locomotive chassis.

The adaptor is simple to make and works well, but by its very nature, an 8-pin plug will not enable all functions of a 21-pin decoder to be used. This is unlikely to be an issue in most cases, as 8-pin chassis locos tend to have few built-in functions.

If used with a sound decoder, separate wires will need to be soldered to the adaptor for the speaker connections; the schematic below shows the relevant solder pads. Alternatively, in some cases, speaker wires can be soldered directly to the chip.

Download a free PDF file of the wiring diagram here:


Items required for this simple project are:

– MTC 21-pin breakout board (e.g. Laisdcc or ESU)
– 8-pin plug (pre-wired, if possible)
– Reel of decoder wire (for non-wired plugs)
– Soldering iron, solder & liquid flux
– Kapton tape or insulation tape
– Various tools, including: small side cutters, wire stripper and an exacto knife.

DCC Decoder Wiring Diagrams for Non-DCC Ready Locomotives

We’re working on a short tutorial looking at DCC decoder installation in older locomotives, such as Lima and Hornby, that are powered by ringfield/pancake-style motors.

To accompany the tutorial, we’ve produced a PDF containing a series of basic wiring diagrams to help with the installation process. They cover the more modern can-style motors (as found in Bachmann, Heljan, Dapol etc.) as well as the older ringfield ones (similar to those found in many Hornby and Lima models).

 

There’s also a basic diagram for directional lighting and a single Aux channel, such as the Aux 1/green wire available on most low/mid-range decoders, such as Hornby’s entry level R8249 8-pin variety.

The wiring principles would be the same for older ‘grain of wheat’ bulbs, although the resistor value would need to be altered to suit the bulb and track voltage.

You can download the PDF by clicking here.

Tutorial: TCS 21 Pin DCC Breakout Adaptor

In our last blog post, looked at the TCS-brand 21-pin breakout board, which can be used to permanent convert an 8-pin DCC decoder for use in a 21-pin chassis.

21 Pin DCC Breakout Adaptor Pinout Wiring Diagram

We’ve now put together a short YouTube video on how to carry out the modification, which you can watch below. We’ve also produced a wiring diagram to accompany the tutorial, which is available by clicking here.