CM400A headlight not working, other lighting issues

amaj89

New Member
Joined
Jul 23, 2026
Total Posts
6
Total likes
0
Location
Canada
Hi everyone,

First post here.

Got a 79 CM400A and looking for some wisdom and solutions.

Last night I had the idea and taking off the gearlight gauge and rest of the dashboard -- keeping the sped, choke, and ignition key slot - purely aesthetic.

I went ahead and took them off and successfully reattached what I wanted to keep, but the second I turned the key, my headlight didn't turn on. I taped all the wires I couldn't remove.

Brief history:
- when I got the bike, the headlight wasn't working. replaced its fuse and good to go
- this recent "project" I did killed that headlight, so I figured it was probably the fuse. changed the fuse but no luck. went ahead and reattached everything back to stock

Here's my issue now:
- gear gauge lights are off (neutral reads as "1", "1" as "2", and "2" as Neutral)
- headlight still not on

Now I am aware of this black wire and figured it could be that, but even after reattaching everything, I'm left with this.

So, if there is a way to fix this please let me know. And if there is a way to manage keeping only my sped and removing my gear gauge and dash lights, please let me know.

It's my first ever electrical "project" so I'm learning as I go.

If I forget anything, I'll put a reply.

Thanks in advance,

Aaron
 
UPDATE:

Got it working again -- had to reconnect the gear gauge wires to different connections (not Brown/Red to B/R, etc etc) -- is this common? Headlight swapped with my 81 and lit up. I had to reconnect everything cluster-wise again and learned its not meant to be toyed with so long as you're seasoned with CM400A's and an electrician.

What a mess the wiring is. I wish I could make it more accessible.

Unnecessary project but signficant lesson learned and skills earned.
 
First thing you need is this (yeah, it says 1980, but they're the same for the issues you're dealing with)

1784779848357.png


In particular this section here for the gear indicator.
1784780021838.png

These three bullet connectors here are just connected out of order. They get faded and dirty with age and identifying the color can be problematic.

For the headlight, You've likely disconnected this ground wire:
1784780396207.png

The headlight power comes out of the fusebox via the black and yellow wire, into the handlebar switch, low beam is the white wire coming out, high beam is the blue.

As you can see from the diagram, power and ground wires daisy chain a lot in the honda schematic. If you start randomly disconnecting stuff without understanding how it ties into the rest of the grid, it can cause issues in other places.
 
amaj89 said:
UPDATE:

Got it working again -- had to reconnect the gear gauge wires to different connections (not Brown/Red to B/R, etc etc) -- is this common? Headlight swapped with my 81 and lit up. I had to reconnect everything cluster-wise again and learned its not meant to be toyed with so long as you're seasoned with CM400A's and an electrician.

What a mess the wiring is. I wish I could make it more accessible.

Unnecessary project but signficant lesson learned and skills earned.
Click to expand...
Those gear indicator lights are flipped at the other end then. 1784780749783.png
 
EzPete said:
Those gear indicator lights are flipped at the other end then. View attachment 59675
Click to expand...
I see.

Thanks for your help, EzPete.

I have the book so I've seen this diagram. Much appreciated for pointing this stuff out for me. I figured it was the ground and you pointing that out and theorizing the same is great, though I don't know what I'd do with this new knowledge but that I shouldn't fool around with this stuff.

So, on this note, is it possible to then keep the headlight and remove the gear gauge (heavily doubt I would ever try after this, but just curious)?
 
You can absolutely remove the indicator light panel, you just have to remove only the components and wires that pertain to it. There are a ton of youtube videos on basic 12V DC automotive electrical that can give you the basics to understand what that wiring diagram says. I'd start there so you have a basis to work from when dealing with the electrical on your bike.
 
amaj89 said:
I see.

Thanks for your help, EzPete.

I have the book so I've seen this diagram. Much appreciated for pointing this stuff out for me. I figured it was the ground and you pointing that out and theorizing the same is great, though I don't know what I'd do with this new knowledge but that I shouldn't fool around with this stuff.

So, on this note, is it possible to then keep the headlight and remove the gear gauge (heavily doubt I would ever try after this, but just curious)?
Click to expand...
Be careful what you remove! The gear switch feeds the change relay which feeds the CDI. All of that stuff works on the timing change from neutral to drive.
 
EzPete said:
You can absolutely remove the indicator light panel, you just have to remove only the components and wires that pertain to it. There are a ton of youtube videos on basic 12V DC automotive electrical that can give you the basics to understand what that wiring diagram says. I'd start there so you have a basis to work from when dealing with the electrical on your bike.
Click to expand...
Beautiful, thank you.
 
You must log in or register to reply here.
Back
Top Bottom