MS2-Extra Neon/420A Manual

Only for use with the MS2-Extra code (HC9S12C64 based microprocessor - MS2 Daughter Board)

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NOTE: Please ensure you have one of these daughter boards inside your ECU before continuing. If you have a black microprocessor, then you have an MS1 and these manuals are NOT for MS1 see here for MS1-Extra Manuals

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Please Note:

All of these instructions / diagrams are to be used at your own risk, like most things there is more than one way to do the same thing, what we have tried to do is to offer a method that we have tested or that others have tested for us. No warranty expressed or implied.

Use at your own risk.
If you do have any suggestions or settings that work please let me know Philip.Ringwood(at)

Main Index of MS2-Extra Manuals

Layout of Components -- Suggested Supply points -- List of common components and part numbers


Wiring for the Neon / 420A Decoder -- Settings

The "Neon/420A" mode theoretically supports the following vehicles when equipped with a 2.0 or 2.4 4cylinder Chrysler engine.
"NS" body models:
1996-2000 Chrysler Town and Country
1996-2000 Dodge Caravan/Grand Caravan
1996-2000 Plymouth Voyager/Grand Voyager
"JA" body models:
1995-02 Chrysler Cirrus
1995-02 Dodge Stratus
1996-2000 Plymouth Breeze
"JX" body models:
1996-02 Chrysler Sebring Convertible
"PL" body models:
1995-02 Dodge Neon
1995-2001 Plymouth Neon
"PT" body models:
01-02 Chrysler PT Cruiser
"FJ" body models:
1995-02 Chrysler Sebring Coupe
1995-2000 Dodge Avenger

Wiring for the Neon / 420A Decoder

Circuit Diagram for V3.0 PCB:

Wire the Megasquirts ECU's input section up as per this diagram in the input wiring section:


Circuit Diagram for V2.2 PCB:

Wire the Megasquirts ECU's input section up as per this diagram in the input wiring section:


Setting the Software for Neon/420A


Ensure the settings are as above


Spark output comes on D14 and D16 see HERE for options on driving the coils.


Suggested points for Supplies inside the V3.0 ECU



Component Pinouts

Pull up circuit diagram

List of component part numbers used in the ignition section:

DigiKey part numbers:
Farnell part numbers

2N2222A = 497-2598-5-ND
1N4001 = 1N4001/4GICT-ND
1K resistor = 1.0KQBK-ND
470R resistor = 470QBK-ND
2K resistor = 2.0KQBK-NB
330R resistor = 330QBK-ND
680R resistor = 680QBK-ND
200R resistor = 200QBK-ND
270R resistor = 270QBK-ND
1K5 resistor = 1.5KQBK-ND
4K7 resistor = 4.7KQBK-ND
0.01uF Cap = P3103-ND
4N25 (opto) = 4N25ASHORT-ND

2N2222A = 920-7120
1N4001 = 352-5326
1K resistor = 509-164
470R resistor = 543-305
2K resistor = 543-457
330R resistor = 543-263
680R resistor = 543-342
200R resistor = 543-214
270R resistor = 543-240
1K5 resistor = 543-421
4K7 resistor = 543-548
0.01uF Cap = 389-0995
4N25 (opto) = 102-1090

Please note: Above part numbers will need checking, some components will come with a minimum order in multiples of 5 and 10.

If you have a question, comment, or suggestion for this FAQ please post it on the forum.

No part of this manual may be reproduced or changed without written permission from James Murray, Ken Culver and Philip Ringwood.

Murray, Ken Culver and Philip Ringwood.