Topic: CB400f Blowing Main Fuse

[jakec]

Hi guys, just got to working my new 400 that you may have noticed me prematurely bragging about here on the forum...

Took possession of this bike last week on Wednesday, and the battery arrived Friday. Juiced it up and charged it over night. Saturday morning I went to start it for the first time. Turned the key and the lights come on. Headlight, neutral, and oil. Never had an oil lamp before so I pull the dipstick and yes, there is oil. Although it is dark,

Press the starter, get about 1/10 of a second of starter motor cranking noise and it goes quiet. Obvious blown fuse so I removed the cover and discovered that the main fuse was (was) a 20a in a 15a slot and it was severely blown.

Below are the fuses that I've gone through since. First one is on bottom.



So far I have checked the battery terminal connections and file and cleaned them. I have also tried a different battery.

I have cleaned the main fuse terminals and checked all of the other fuse terminals.

I have checked all exposed wires and connections and they are clean and not worn so far as I can see.

New battery:



The motherboard:



Freely dangling flasher?




I have also opened the right hand controls and everything looks clean. You can however see, if you use your imagination, how the black lead for the starter is showing a tiny bit of copper, and it is pretty close to the solder on the yellow and red lead. Possible culprit?



I have not tried disconnecting the headlight yet. There is no option to have it turned off on this bike. I haven't tried disconnecting the ignition and bypassing it either. I just haven't had time yet.

[calj737]

On your right hand control, that Black wire provides switched 12v to the Yellow/Red for the START button.
The "dangling" Green wire under the left side panel is an extra Ground wire; normal.

I'd check the BLACK/WHITE wires from the KILL/RUN switch to the coils. These carry power to the coils. Disconnect them, try hitting the START again and see what happens. If that doesn't identify the issue, for giggles kickstart the bike with the coils connected. Fuse blow?

[Flyin900]

That green wire shouldn't be on the flasher the black and grey only. The green is a spare and not connected. May not be anything related to you problem, but is incorrect in the way it is presently wired. The grey wire is the +12V and the green is a ground, so you have a dead short there. The dangling black wire needs to be put on the flasher and the green one removed.

[calj737]

That green wire shouldn't be on the flasher the black and grey only. The green is a spare and not connected. May not be anything related to you problem, but is incorrect in the way it is presently wired.
The dangling black wire needs to be put on the flasher and the green one removed.

Good eyes there, Fly. Interesting, disconnecting the Green from the Flasher Relay, will make 2 loose Grounds. I wonder if his Regulator is connected? Fly is right; the loose Black connects to the Flasher with the Grey carrying power to the handlebar controls.

[Yamahawk]

Actually, it appears that he is using a 3 prong flasher relay. The black wire is connected to the 3rd terminal on his flasher, along with the green and grey wire. I am using a 2 prong flasher, and so I don't use the green wire at all. However, I have seen the stock Honda flasher for my CB750, and it has 3 prongs too...and uses the green.
Jake, is that the stock flasher that is in there, or did someone replace it with an aftermarket flasher? It might be that it needs the 2 prong flasher, and leave that green disconnected. Just for a test, pull the green wire as has been suggested, and see if it stops fuses being blown. Then, see if the flasher still makes the turn signals work properly. If everything works, cool, if not, get a 2 wire flasher and hook it up with the black and grey wires, and leave the green unhooked.
Charlie

[jakec]

Thanks for all the replies.

The flasher: when I got the bike the green was disconnected from the flasher just dangling there. I hooked it up to the flasher AFTER I blew the first fuse because I thought it might be part of the problem. It's been hooked up ever since. I can try disconnecting it tonight.

For the kill/run switch: I can't even try pressing start right now because it blows the fuse as soon as I turn the key to the ON position.

My plan for tonight was:

-check headlight bulb

-bypass ignition switch

-check starter button for arc when turning key on

I can tank the tank off and start looking at the cools and rectifier, regulator etc after all that if I am still not finding any clues.

[calj737]

For the kill/run switch: I can't even try pressing start right now because it blows the fuse as soon as I turn the key to the ON position.

Well there's a clue... You don't have to remove the tank to access the coil wires, but it is slightly cramped under there. Where the BLK/WHT wires exit the handlebars, disconnect the single BLK/WHT lead, then press START. If the fuse doesn't blow, odds are you've found the circuit that is the culprit.

[strynboen]

try to remove the green from the flasher(just for test)..and put a big bulb 55W instead od the main fuse..to safe you for bloving all those fuses..then the light vill just flash..as long the short is there..and glow ,,vhen all is ok.....
after the problem is faund ..thange back to the korrekt fuse....the problem is in the main fuse elektric  power line,,so only a few Things is direkt on this line..so thek those up..and thek for broken isolation..or shorted up parts..like the regulator or ignision system..and try to de konnekt them..and try Again..

the test bulb can be made of a old car bulb..and some viring..need to be abaut 40-55watt to take a lot of power load..for this test

[jakec]

Sorry, not sure how I forgot to mention that. Yes, the first time I turned the key the lights came on and the fuse didn't blow until I pressed the starter button. However every time after that it would blow as soon ad the key was turned. That's why my "real life" friend has suggested that I route around the key switch to rule it out.

Can you elaborate on the black/white wires? Which ones do you mean?



I think I will be taking the tank off as I don't want to scratch it while working. Plus, No crossover line 

[strynboen]

that start safty rectifire(diode)..looks like a problem maker..it can make a direkt short..if there is a Loose vire...there is both ground and positive battery at the same unit..so thek you not have the falce green on there...mine 400 is the erlyer euro model..so i can turn the light off..and dont have that viring for auto off light

try to take the power of the diode..and see if the fuses then hold up

[FuZZie]

the first time I turned the key the lights came on and the fuse didn't blow until I pressed the starter button. However every time after that it would blow as soon ad the key was turned.

yea but if the switch was shorted it would just engage the starter. Your at starter or solenoid, maybe stuck engaged from sitting or a PO issue?

[jakec]

Ok, good point, if it arced then it would engage the starter. But what if arcing and engaging the starter is instantly causing the fuse to blow?

I don't see the ignition (key switch) anywhere on this diagram, but I do see all three wires attached to the blinker relay.

The solenoid is the thing below/to the left of the fuse bank, right? I checked under the rubber hood and all of those connections look great. Is the rectifier the black plastic box thing with fins/ridges on it? I checked that too and everything is just so damn neat and tidy..

I do believe that this bike sat for a while while under previous ownership. However he promises me that he started it before the shippers took it away from him. I asked him about this issue and he said he had not had this issue with the bike (which I sort of believe since all the lights were coming on the first time I turned the key). He suggested that I check the housing for the right hand controls and see if there was a short there, but I don't see one.

[jakec]

I see the cartoon keyhole now...

I prefer this style for the diagram, easier for me to read.

[calj737]

I see the cartoon keyhole now...

I prefer this style for the diagram, easier for me to read.

On this diagram, the coil wires are connected to the “Emergency Switch” (top center of diagram). The key switch is at the bottom, directly in front of the HORN.

[FuZZie]

They look like oldmanhonda to me cal

[calj737]

They look like oldmanhonda to me cal

Agree.

[Bodi]

Please use an actual Honda wiring diagram. All the Haynes, Chilton, and internet colored ones are shyte. Mistakes plus stuff just left off for no good reason, I suppose it simplifies the drawing? Not so simple when you have a problem with something the buggers left out.
If it blows the fuse immediately on key ON but didn't originally... weird.
The starter safety diode is not your problem. If it fails "short", you just get the N light on whenever the clutch lever is pulled in. Makes it less easy to find neutral.
The flasher green wire... some 3 terminal flashers don't use ground, the 3rd terminal is maybe a second signal light out or for an idiot light - regardless, the fuse pops with key on if connected to ground (been there). test with it off.
The light bulb wired to the fuseholder is a great way to find shorts.

[FuZZie]

Try this one
http://manuals.sohc4.net/cb400/technical_reference/WD40075.jpg

[jakec]

Tonight I removed the headlight to look in the rat's nest and everything looks normal except for a brown wire female connector which isn't connected to anything. I see that shown in the wiring diagram above, though.

The headlight's three prongs were a little bent and one was only hanging on by a thread so I am currently using epoxy to fix that.

What I tried tonight was headlight off (disconnected), and the fuse still blew. Then I jumped the ignition, by putting a wire from the red to the black on that -pin connector, and the fuse also blew.

Checking and rechecking everything and it's all connected and very clean, with the exception of that one headlight connection prong. I have not taken the tank off yet to look and see what's happening under there. I am really thinking that it should be being cause by the starter switch since that's what started it all (the fuses blowing I mean).

[Flyin900]

The brown wire is off the ignition switch and is an unused wire that can run an accessory that is switched. You do need to remove the tank and look at the large wire bundle that will contain both the wiring from the run switch on the right side and the left hand switch. It seems you have a dead short that is blowing the fuse once the ignition is turned on.
Here is a picture of the black wire bundle and it's location on the left side of the has tank.

[jakec]

If it blows the fuse immediately on key ON but didn't originally... weird.

The flasher green wire... some 3 terminal flashers don't use ground, the 3rd terminal is maybe a second signal light out or for an idiot light - regardless, the fuse pops with key on if connected to ground (been there). test with it off.

I just went down and unplugged the ground from the flasher. I tried with kill switch on and off, the fuse blew just the same both times.

[jakec]

The brown wire is off the ignition switch and is an unused wire that can run an accessory that is switched. You do need to remove the tank and look at the large wire bundle that will contain both the wiring from the run switch on the right side and the left hand switch. It seems you have a dead short that is blowing the fuse once the ignition is turned on.
Here is a picture of the black wire bundle and it's location on the left side of the has tank.

What should I be looking for when I look at the main loom under the tank? Sorry I have only had this bike for about a week and i've barely touched it (kind of afraid because its so nice). My CL175 only has one fuse and a lot fewer lights and things to keep track of.

[Flyin900]

The problem is in the starter circuit I think. Does the fuse blow when the ignition is just turned on and nothing else is pushed? ie starter button is not pushed? If the fuse is blowing as soon as you turn the ignition on then there is a dead short somewhere either in the ignition switch or in the right hand switch or the solenoid.

[calj737]

The problem is in the starter circuit I think. Does the fuse blow when the ignition is just turned on and nothing else is pushed? ie starter button is not pushed? If the fuse is blowing as soon as you turn the ignition on then there is a dead short somewhere either in the ignition switch or in the right hand switch or the solenoid.

To be specific, does it blow when the KEY is turned ON, or, when the KILL/RUN switch is turned ON, or, ONLY when the START button is pressed?

The lights will not cause the MAIN fuse to blow (as Bodi said). If the fuse is blowing when the KILL is moved to RUN, then its the coils. If it blows when the START button is pressed, its the BLACK>Yellow/Red to the solenoid circuit. Easy to isolate.

[jakec]

First time (Saturday) it only blew once the starter button was pressed. But every time since then it has blown as soon as the key is turned to ON. Whether the KILL is in the ON position or the OFF position, the fuse blows as soon as the key is turned to the ON position.

I can turn the key quickly past ON to PARK and the fuse won't have time to blow. But it will get real bent out of shape. 

I bypassed the ignition switch tonight and it still blew. If it were a short in the right hand switch, what would that look like?

My friend has suggested that I disconnect the solenoid to try and eliminate that. I was planning to try that tomorrow night (need to buy more fuses).