How to fit a decoder to a loco with an 8-pin NEM 652 socket
Fit a plug-in decoder to a 'DCC ready' OO or HO loco with the common 8-pin socket, getting pin 1 right first time and testing before you refit the body.
- Time
- 30 minutes
- Difficulty
- Easy
- Cost
- Moderate cost
- Steps
- 7
- Checked
What you’ll need
- An 8-pin (NEM 652) plug-in decoder
- Small screwdrivers Search Amazon for precision screwdriver set
- Double-sided foam tape Search Amazon for double sided foam tape
- Kapton or insulating tape Search Amazon for kapton tape
- Magnifier Search Amazon for magnifying glass with light
As an Amazon Associate we earn from qualifying purchases. The Amazon links go to search results, so you can compare what’s available.
Before you start
- Work with power disconnected (ESU).
- The NMRA says the loco side must never link the motor to the track pickups or chassis – a decoder fitted to such a loco can be damaged immediately.
Step by step
-
Step 1: Check the loco on DC
Run it on analogue first and fix any rough running – ESU says only a loco with faultless mechanics is worth converting.
Next: step 2 -
Step 2: Remove the body and find the socket
The 8-pin socket is two rows of four on 0.1 in pitch (NMRA S-9.1.1.1). Find the pin 1 marking – *, +, dot or 1.
Next: step 3 -
Step 3: Know the pinout
Pin 1 Motor + (orange), 2 rear light (yellow), 3 AUX1 (green, optional), 4 left rail (black), 5 Motor − (grey), 6 front light (white), 7 common + (blue), 8 right rail (red) (NMRA S-9.1.1.1). The decoder's orange wire marks its pin 1.
Next: step 4 -
Step 4: Swap the blanking plug for the decoder
Keep the dummy plug safe. Check the decoder pins are straight, align the orange-wire side with pin 1 and press in gently. The plug will physically fit both ways round, so the mark matters.
Next: step 5 -
Step 5: Position the decoder
Keep components away from metal, fix with double-sided tape or a little hot glue, and don't wrap it in tape (ESU).
Next: step 6 -
Step 6: Test on the programming track
Read CV1 and CV8. Then test on the main at address 3: forward, reverse, lights.
Next: step 7 -
Step 7: Refit the body carefully
Tuck the wires so nothing rubs on the motor, flywheel or gears.
Tips
- The 8-pin socket is rated 1.5 A per pin continuous, 3 A peak (NMRA S-9.1.1.1).
- Write the loco's new address on a label under the chassis.
When to get expert help
For locos without a socket or with the motor not isolated from the frame, ask a model shop or DCC installer.
Questions people ask
The loco runs but the lights don't?
The plug may be in the wrong way round or the loco may use the blue common differently. Re-check pin 1.
Do I need a programming track?
It's the safest way to check the decoder before you run it, and some CVs (such as long addresses on ESU decoders) need it.
Sources
Checked 18 October 2026. We wrote this guide in our own words, using:
- NMRA S-9.1.1.1 Six and Eight Pin Decoder Interface (nmra.org)
- NMRA S-9.1.1 Decoder Interfaces (nmra.org)
- ESU LokPilot 5 instruction manual, Edition 7 (distributor copy) (intermountain-railway.com)
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Printed from dcctrainautomation.uk/guides/fit-a-decoder-to-an-8-pin-nem652-loco/ · Checked 18 October 2026 · General information only. Follow the maker’s instructions for your own equipment, and keep mains wiring inside properly made, enclosed power supplies.