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Discussion Starter #1 (Edited)
Honda CM400C - Neutral Light Issue (SOLVED)

Hi All,


I'm wondering if anyone can help point me in the direction of some troubleshooting tips.

Long story short..
I bought a Honda CM400C in 2015 as my first project bike.
Everything was removed from the bike until in was in 100's of pieces!
Over the past year I have been building the bike bit by bit on the weekends.
And finally... I'm nearly there !

My current issue -

The Neutral light is not lighting up when in Neutral.
I have installed an aftermarket speedometer with the warning lights featured inside.
I know for a fact that the neutral light is wired correctly and that the warning light on the speedo is working.

Where else can/how I check that other connections are correct?

e.g.
Do the wires on the clutch connect to the neutral light?
Could the neutral switch be faulty?
Could the neutral switch wiring be wrong?
(How can I check these?).

And finally, will this prevent the bike from starting?
I'm looking at trying to fire her up next week, but I have a feeling this issue might prevent the ignition?
Would that be correct?

Any help and guidance would be much much appreciated.


Kind regards,

Nick.

Pictures - From the day of purchase to this mornings current progress.

1.jpg

2.jpg
 

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Hi there!

I will try to help you as I also did an aftermarket speedometer install. First you should check if the speedo receive positive or ground to activate the neutral light. In the stock cluster the neutral light will receive a ground signal from the neutral switch, so if your aftermarket speedometer does need a positive signal you will have to use a relay to make it work.

I've posted a simplified wiring diagram as I've come to understand more how it works:
http://www.hondatwins.net/forums/showthread.php?t=65169

Both the clutch switch and the neutral switch perform the same function on the bike: provide ground for the starter relay. Either one or the other needs to be activated so you can start the bike.

You can also test the neutral switch with a multimeter on continuity mode. One end grounded and the other on the switch and fiddle with the gear lever until you find neutral, then it must beep.

Also: damn cool bike you've built there! Let me know if you have any questions!
 

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Pretty much as above. You need power from the ignition switch (with the switch on) to the neutral light. Connect the other terminal on the neutral light to the neutral switch. With that wire disconnected from the switch and connected directly to ground the light should illuminate. If it doesn't you have a problem with the wiring. If it does, but not when connected to the switch when in neutral, you have a problem with the switch.

Just for reference:

file:///C:/Users/Justin/Favorites/Downloads/Honda%20CM400T%20Wiring%20Diagram%201979.pdf
 

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There is one other piece that may be missing since the bike was in pieces. There is a silicon diode in the starting circuit that if missing disables the starting. You'll find it in the wiring harness on the left side by the regulator. Small little black box with a 2 wire connector. Rarely ever fail but if missing the electric starter won't work.
 

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Discussion Starter #5
Hi gents,

Many thanks for all the replies.

I really do need all the help I can get to finish the project!

I have unveiled the wiring I had done for the speedometer install to check it was all correct to eliminate that angle.

Everything seems in order..!

I failed to mention that the speedo backlight was working when I first did the speedo install but now seems to have no life!! (confusing!!).

I have attached some images below of the current neutral switch wiring, could you check to see if I have the correct connections?

Please guide me to my next fault finding steps !


Aftermarket speedometer wiring diagram
Screen Shot 2017-03-06 at 08.01.00.png

Speedo neutral light wiring
[From Speedo] -Black/Red > -Black [To Harness]
[From Speedo] +Green > +Light Green/Red [To Harness]
IMG_4158.JPG

Clutch switch connection
Green > Left connection (When facing front of bike, looking towards the back)
Dark Green/Red > Right connection (When facing front of bike, looking towards the back)
IMG_4156.JPG

Neutral switch connection
Light Green/Red > To Switch
IMG_4157.JPG
 

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Discussion Starter #6
PS.

While working on the engine, both side cases were removed.

Could this have effected anything on the neutral switch side?
 

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Reading the wiring directions for the speedo.
Neutral light should be wired as Honda Black to Gauge Green and Honda Lt. Green w/Red to Gauge Green w/Black
Speedo back light should be wired Honda Brown w/White to Gauge Orange and Honda Dark Green to Gauge Black.
The clutch safety switch doesn't care which wires are where. For the time being to eliminate a possible bad switch use a jumper wire between the 2 spade connectors, a blade type fuse works good. Just be sure the bike is in neutral before starting.
Test your neutral switch by using a VOM set for ohms, one probe to the battery negative terminal and the other to the switch top terminal. In neutral you should have almost no resistance, there'll be a little, and in gear it should show infinite or open circuit.
 

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Discussion Starter #9 (Edited)
Hi All,


Sorry for the delayed reply.


Update -

I have doubled checked all the wiring of the neutral switch.

All seems as it should, thats at the speedo and at the actual switch.

I also removed the switch to check it wasn't sitting incorrectly/damaged.

Still nothing :(

I will test the neutral switch as suggested by longdistancerider (many thanks for the advice!).

I'll need to obtain a multimeter first!

As mentioned before, I removed the side cases from the engine.. Would that have changed the switch neutral alignment at all?
Because all the connections are correct and I can't understand why the switch would just fail?
Could it be that when in neutral the switch is not registering because I have missed something when reinstalling side cases?



In other news..

I have managed to get the speedo backlight working!

It was due to the Low/High Beam Headlight Switch !!

The little white switch which you flick with your finger wasn't sitting/connecting correctly.

It was effecting the headlight bulb, the speedo backlight & the indicators! (all intermittently on/off!).

I shaved a few mm from the back of the switch using the dremel and now its sits much better and all lights are working fine!


Thanks for everyones help.
Forums like this are a massive help to us beginner enthusiasts.
 

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The neutral switch mounts to the upper crankcase and is not exposed when the side cover is removed. No way what you describe having done would affect that. Of course it is always possible for the switch to fail all by itself, they do that.

You can also test the switch with a test light rather than a multimeter if you have one of those. Disconnect the wire from the switch. Connect the test light alligator clip to the positive battery post and touch the probe to the wire terminal on the switch. When in neutral the light should come on, when not in neutral it should go out.
 

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Discussion Starter #11
The neutral switch mounts to the upper crankcase and is not exposed when the side cover is removed. No way what you describe having done would affect that. Of course it is always possible for the switch to fail all by itself, they do that.

You can also test the switch with a test light rather than a multimeter if you have one of those. Disconnect the wire from the switch. Connect the test light alligator clip to the positive battery post and touch the probe to the wire terminal on the switch. When in neutral the light should come on, when not in neutral it should go out.
Hi JT,


Many thanks for the advice!

I followed your steps, and you are right.

When in neutral the test light comes on, and when in gear the test light goes off.

IMG_4195.JPG

Would I be right in thinking that this proves that the neutral switch is actually working?

I can't think of where to go now -

1. It seems all the connections are correct
2. It seems the neutral switch is working
3. The indication light on the speedo is working when tested

Any ideas to help would be massively appreciated.


Thanks,

Nick.
 

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The light needs to find ground from the neutral switch ONLY. So, you need to have power going TO the neutral indicator bulb when ignition is on, but no other source of ground but the trans switch.
 
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Now ensure that you have 12v power to one side of the neutral indicator light when the ignition switch is on and not when it's off. The other terminal on the indicator light should be wired to the switch and the light should come on when that wire is grounded. If it doesn't that second wire is your problem.
 

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Do the same test again BUT this time go to the gauge wire connection, this will test the entire circuit. There is a bullet type connection in a big rubber boot above the battery that may be disconnected.
 

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Discussion Starter #15
Hi All,

Thank you all so much for the replies.

I have managed to have another investigation this morning.

I tested the Light Green/Red wire at 1. The Speedo 2. The Rectifier.

Bother showed the same conclusion - Test light came on when in Neutral, Test light went off in gear!

Would I be right in now thinking that this means there is power going to the speedo, so issue is with the black wire?

I have a wire diagram, which I will attach below.

I can't seem to trace the black wire and what is it's function?

What would you suggest next?

Sorry to be a pain !!


Wiring Diagram
View attachment Honda CM400T Wiring Diagram 1979.pdf

Testing Light Green/Red wire at the speedo
IMG_4213.JPG

Testing Light Green/Red wire at the rectifier
IMG_4212.JPG
 

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Discussion Starter #16
PS.

I installed an Indication Relay as the new indicators are LEDs.

Note sure if this would cause an issue?

I have attached an image below..

It shows that the black wire from the old relay wasn't needed for the aftermarket relay, so it has been left unconnected.

IMG_4214.JPG
 

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The Black wire is a main power feed coming out of the ignition switch for things like horn, turn signals, starter solenoid. All the basic operation and safety equipment.

Correction to earlier post. Brown w/White is for ON position of the ignition. Brown is for the Park position on the switch
 

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Discussion Starter #18
Any suggestions as to what the issue could be?

There is power going to the LED via the BLACK WIRE and there is a signal from the neutral switch va the GREEN/RED wire!

Has anyone wired one of these speedometers in a similar situation?

I have researched this over and over and can't seem to determine the issue at all.

Some forums have suggested that the switch needs to be grounded..? Which I have tried but zero luck!

Also, would there be a way to wire this outside of the loom?

Example -
Wire from neutral switch straight to - speedo neutral warning light.
Power wire going straight to + speedo neutral warning light.

Many thanks,
 

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Discussion Starter #19
Hi All,


It seems I have.. FIGURED OUT THE PROBLEM !!

Was it simple..? Yes.

Should I have thought of this..? Yes!


Referring to the speedometer manufacturers wiring diagram below -
Screen Shot 2017-03-06 at 08.01.00.png

It clearly states..

NEUTRAL
(+) GREEN WIRE
(-) GREEN / BLACK WIRE

WRONG !!!

It should be wired the other way around !!

I cut the wires to test the bulb (started to doubt myself), and of course the bulb was working!

While the wires were cut I thought I would test the circuit the other way around and BANG - WORKS!

Special thanks to -

- dirceucorsetti
- J-T
- longdistancerider
- dtsmjr8dan


For all your help & replies.

Hopefully this thread will help others who encounter this issue!


Regards,

Nick.
 
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