Last Updated: 16 June 2025

How to Convert Graham Farish Class 66 66623 (371-394) to DCC

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This guide covers the following models:

DCC Ready PCB Conversion

This guide covers the Graham Farish Class 66 diesel loco which has a DCC-friendly PCB. The conversion requires removal of two brass clips, and the soldering of seven wires onto the correct solder pads on the PCB.

For the full guide, follow the 7 wire PCB method. For this model, a Doehler & Haass PD10MU-3 decoder was used which is small enough to tuck in under the lighting wires at the long cab end. This decoder also has a lighting common solder pad, onto which the blue wire (solder point #7) has been connected. The conversion can also be done with using an ESU LokPilot 5 Micro.

Step 1 - Remove body

Remove the body by gently prising the body away from the chassis and pulling upwards.

Convert Graham Farish Class 66 with DCC-ready PCB to DCC

Step 2 - Remove copper clips

Locate the two copper clips in the bottom right hand corner of the PCB. They have numbers 8, 1, 2 and so on immediately above them. Remove the clips to reveal seven solder points.

Step 3 - Connect decoder

Connect the wires in order according to the table below. If your decoder does not have a lighting common (blue) wire, you can connect a small bridging wire between solder point #7 (blue) and #8 (red). The decoder will tuck in underneath the lighting wires. You can optionally use a small piece of black tack to secure it. Make sure the decoder is suitably isolated from any metal parts of the chassis using some tape.

Graham Farish DCC Ready PCB Wiring Diagram
PCB Pad # Colour Decoder Pin # Description
1 Orange 1 Motor (right)
2 Yellow 6 Lights direction 1 (-)
4 Black 4 Track Power (left rail)
5 Grey 2 Motor (left)
6 White 5 Lights direction 2 (-)
7 Blue n/a Lights common (+)
8 Red 3 Track Power (right rail)

Step 4 - Test

Place your loco onto your test track and read the loco ID. It should shuffle a few times and then come back with the default loco ID of 3. You can then try running the loco backwards and forwards, and check that the directional lighting is working correctly.

Convert Graham Farish Class 66 with DCC-ready PCB to DCC Convert Graham Farish Class 66 with DCC-ready PCB to DCC

Step 5 - Refit Body

Refit the body and you are done!

Convert Graham Farish Class 66 with DCC-ready PCB to DCC