Mistakes may damage your locomotive, controller or other accessories. Use a multimeter to make absolutely sure you have completely isolated the motor from the track before testing. Always use the Programming Track for testing. Our guides are provided for reference only, and you proceed entirely at your own risk. Unsure about something - try our DCC Conversion Service instead.

This guide covers the older Poole-made Graham Farish Class 91 electric locos in Intercity livery, including:

• Class 91 91004 Intercity (8807)
• Class 91 91005 Intercity (8807)
• Class 91 91007 Intercity (8807)

The conversion requires two brass sleeves replacing with isolated ones. The procedure is basically the same as the Graham Farish insulating bush (Digihat) method, but both the upper and lower parts are live to the chassis, rather than just the lower part.

Step 1 - Remove Body

Remove the body by pulling gently upwards. Undo the screws at each end to release the chassis blocks that are holding the bogies in. Drop the bogies out and put them to one side.

Step 2 - Prepare Chassis

Turn the loco upside down. Remove the capacitor by slightly unscrewing the screw that traps one leg, and desolder the other.

Drill three small holes in the top surface of the black plastic moulding, two on one side of the chassis and one on the other. These will be used to neatly pass the wires from inside the loco body to the underside of the chassis, without being visible.

Step 3 - Connect Track Power

Solder a red wire to the central point on the copper strip where the capacitor leg was previously soldered to. Pass the red wire back up through one of the holes drilled in Step 2.

Create a loop of bare wire (black insulation) just slightly larger than the diameter of the screw that was previously holding the capacitor leg in place. Tin the loop of wire, then trap it under the screw and tighten. Pass the black wire up through one of the holes drilled in Step 2.

Step 3 - Isolate Lower Motor Connection

Move the brass arm so that the brass bush can be removed. Take care to make sure the spring doesn't fly out. Remove the spring, the carbon brush and the brass bush. Replace the brass bush with the plastic digihat.

Add a small piece of heat shrink tubing to the brass arm so that it can no longer make an electrical contact with the spring.

Solder the grey wire from the decoder to the spring. Put the spring back inside the digihat, then move the (now insulated) brass arm back over the spring to secure it in place. With a multimeter, check there is no continuity between the chassis and the grey wire. Pass the grey wire up through the remaining hole drilled in step 2.

Step 4 - Isolate Upper Motor Connection

Turn the loco back the right way up, and repeat step 3 for the upper brass arm. This time, use an orange wire instead of grey. Check there is no continuity between the orange wire and the chassis.

At this point, you should have four wires - orange, red, black and grey.

Step 5 - Connect Decoder

There is room for the decoder in the blunt end in the 'number two' cab. Ensure the decoder cannot touch the chassis using Kapton tape, black tack, or similar. Here, the decoder being used is a Lenz Silver Mini, but most small N Gauge decoders will fit. See the end of this guide for an example of a Doehler & Haass PD10MU-3 fitted to an identical model.

Routing of the wires is important, as there is not much room inside the body at the top where the pantograph bay is. The wires must not sit directly on the top surface of the chassis, as the body will not quite sit flush. Route the wires onto the edges where the chassis steps down slightly. A bit of Kapton tape can be used to keep them in place.

Connect the four wires to the decoder as follows:

Step 6 - Reassemble

Put the bogies back in place and secure by sliding the chassis block ends over each bogie tower. Tighten the screws and clip the body back on.

Step 7 - Test

Place your loco on your programming track and check it responds. If you find the loco runs in the wrong direction, you can either swap the grey and orange motor wires around, or update CV 29 (easier).

Conversion Using Doehler & Haass PD10MU-3 Decoder

Here are some alternative photos of the same Class 91 model conversion using a Doehler & Haass PD10MU-3 decoder instead of a Lenz Silver Mini. They also show an alternative wire routing, where the wires are passed down the side of the body rather than through holes drilled in the top of the black chassis moulding. Although not as neat, they are not visible when looking at the loco side-on.

Graham Farish Class 91 Front/Rear Lighting Retrofit

We have succesfully retrofitted directional lighting into the Graham Farish Class 91. Eight LEDs were used: two white and two red at each end. These are grouped and wired to the decoder's front and rear lighting outputs so that the correct configuration of lights are on depending on the direction of travel. For convenience, a connector was added so the lighting-modified body can be detached easily.

Each LED has its own miniature resistor, fitted on the underside of the roof just in front of the pantograph.

Coreless Upgrade

This model can be upgraded to a coreless motor, however some of the chassis needs milling out so the motor can sit completely flat.

Our DCC Conversion Service