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Discussion Starter #1
Hi guys,

My girlfriend bought her first bike a few weeks ago, an 81' CM400C, there is an issue with the tail light not being lit when the bike is switched to ON. The bulb itself is not burnt out, its a dual purpose bulb with 2 filaments inside, both filaments work.

The when the bike is switched to ON, the brake light will work when compressed but the tail light will not work at all. When the bike is switched to accessories the tail light will stay on but the brake light will not function.

It seems logical to assume its a wiring issue, I've nearly replaced the entire harness on my 78 CB400T so i'm fairly familiar with Honda wiring - however I'm just curious if there is anything I should be looking for before I start digging in the bike this weekend.

Is it possible its an issue with how its connected directly to the ignition, or more of an issue down the line closer to the rear end?

Thanks for any help, its much appreciated!
 

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Sensei
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Does the headlight come on automatically when the key switch is on?.....

We KNOW the taillight bulb and the three wires (Brown, Green, and Green with Yellow stripe) running to it are all good...... So the problem, whatever it is, is "ahead" of or within the ignition switch .... Check the headlight/starter switch and the Brown with White stripe wire,,,,,
 

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Sensei
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Again, does the headlight actually come on when you turn the key to "on"?...Yes or NO?
 

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Discussion Starter #5
Whoops, the Headlight works when the key is ON - the headlight does NOT work when the key is on accessories
 

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Sensei
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That's NOT "accessories", it is "park" and ONLY the dimmer taillight filament should be lit, Nothing else on the bike should have power or function IIRC....
 

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Discussion Starter #8
Okay so after staring down the wiring diagram for a bit I think I've figured out whats going on... Correct me if my thought process is broken.

The brown wire from the tail light connects to the ignition, at which point it basically turns into the Brown+White wire and goes up to the gauge cluster and the Hi/Lo headlight switch.

The tail light works, ONLY when the key is turned to Park, tail light does not work when the key is switched to ON. The headlight works when the key is turned ON, but the Hi/Lo switch does not work, and neither does the gauge cluster lights.

When they key is switched to ON it connects the TL2 to the TL1 (Brown and Brown+White), if that were working correctly that means when the key turns ON the gauge cluster + dimmer should work, and it does not.

This means that there is either a short in the Brown+White wire somewhere between the Ignition Switch and the gauge cluster/dimmer, OR it means that the ignition switch is not correctly connecting TL2 to TL1 (Brown -> Brown+White).

How do I test the ignition switch to make sure the switches are being contacted correctly?

If I plan to find a shorted Brown+White wire, do I just grab the multimeter and touch it to the Brown+White contact on the ignition and then to the other end of the Brown+White and see if there is resistance? I'm no electrician so I've never gone hunting for a shorted wire so I probably sound stupid here lol...

Thank you for any help!


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Sensei
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Nope......
When the key is turned on, it energizes the Black wires with B+, one of which goes to the starter switch.....When the starter button is NOT depressed, that B+ travels back to the fuse box via 2 wires, Brown/Blue, and Black/Red...
Brown/Blue is for the taillight, dash and front running lights, and becomes Brown/White after passing through the taillight fuse....

The Brown/White comes forward along the frame and goes to the ignition switch (where it shunts to Brown when key is on, powering the taillight....) It also goes to the left-hand handlebar switch unit where it connects to Baby Blue/White and Orange/White IF the turns signal switch is in its neutral position (lighting the running filaments in the front turn signals only)... Its third connection is to the meter (dash) backlights......

Black/Red is for the headlight and similarly becomes Black/Yellow after passing through the headlight fuse.....
The Black/Yellow also returns forwards, and connects to the starter button switch where it connects to whichever headlight beam (high or low) the dimmer switch position currently tells it to....
When you depress the starter button, the Black/Yellow wires power is shunted from the high/low switch and transferred to the solenoid wire (Yellow/Red stripe), turning the headlight off and the solenoid then connects the starter motor to the Battery +..........

You may phone if further explanation is desired....540-525-5199.... Steve
 

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Discussion Starter #10
Nope......
When the key is turned on, it energizes the Black wires with B+, one of which goes to the starter switch.....When the starter button is NOT depressed, that B+ travels back to the fuse box via 2 wires, Brown/Blue, and Black/Red...
Brown/Blue is for the taillight, dash and front running lights, and becomes Brown/White after passing through the taillight fuse....

The Brown/White comes forward along the frame and goes to the ignition switch (where it shunts to Brown when key is on, powering the taillight....) It also goes to the left-hand handlebar switch unit where it connects to Baby Blue/White and Orange/White IF the turns signal switch is in its neutral position (lighting the running filaments in the front turn signals only)... Its third connection is to the meter (dash) backlights......

Black/Red is for the headlight and similarly becomes Black/Yellow after passing through the headlight fuse.....
The Black/Yellow also returns forwards, and connects to the starter button switch where it connects to whichever headlight beam (high or low) the dimmer switch position currently tells it to....
When you depress the starter button, the Black/Yellow wires power is shunted from the high/low switch and transferred to the solenoid wire (Yellow/Red stripe), turning the headlight off and the solenoid then connects the starter motor to the Battery +..........

You may phone if further explanation is desired....540-525-5199.... Steve
Thanks a ton for your explanation, Steve, definitely appreciate it man! I'm going to read over it again when i'm closer to having a minute to work on the bike and I'll make the right moves at that point - thanks again!
 
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