Honda-SOHC
SOHC.co.uk Forums => CB350/400 => Topic started by: Oggers on April 03, 2020, 01:53:02 PM
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Gents
Bike nearly complete after a modest refresh, but upon connecting up to battery, it blows fuses - the 15A. Neutral indicator lamp glows momentarily, goes out, fuse blown. Tried two more, even a 35A, still blows!
Guess I may have a short somewhere, but I am hopeless at electrics. I do have a multimeter though. Switchgear and headlamp all came apart, so all those connections in the headlamp shell and within the switchgear came apart. I did label them all though beforehand....
Any clues where to start and how to proceed would be most appreciated.
Many thanks
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Impossible to tell without being there. Go over every connection that has been disturbed and double check that it's connected to the right wire. And check all wires to make sure nothing is trapped or damaged and causing your short.
Normally I would say get someone who knows what they're doing to have a look, but not really an option at the moment. 😕
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For a complete novice:
Ignition off.
Multimeter on ohms between fuse and ground. If there’s a short it will show zero or there abouts.
Unplug stuff one at a time and see if this changes. If it doesn’t, plug it back in and move on to the next.
Report back.
Sent from my iPhone using Tapatalk
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First question
Are you fitting the battery the correct way round i.e -ve to earth
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Gents
Steve - done as you say - zero ohms. There is something across the other fuses though....
Bryan - battery connected correctly
Things I have done since
With ignition on
Lamp across the fuse terminals lights as brighly as it does across battery terminals - I guess it should not!
As an aside, I measured the current draw and it seems to be 0.29A as per battery with ignition on - so why does a 35A fuse blow Forgive any stupidity here!
Shorts inside swtichgear could be an issue. Tested all wires from the hadlebars to the bundle on the frame above the head. Pulled each each one off to see if lamp across the fuse dims or goes out - lamp still lit on each one.
Checked all the wires inside the shell. The seem OK, nothing touching any earth point - apart from the 2 green wires which should earth anyways each side of the shell.
Stumpted - Help please! :(
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If you look at the wiring diagram and trace which components are covered by the 15A fuse, that may give you a clue. By what I can see the 15A fuse only covers the starter system and its components but my wiring knowledge is not comprehensive 😊😊😊
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If I may suggest a possibility? A couple of years ago I had a similar situation with the main fuse blowing, but the bike was being ridden fairly frequently, and I had not disturbed anything electrical. I was advised to look closely at the blown fuse, if the fuse wire has parted in the middle of the glass then that indicates a short circuit. If the fuse wire has parted company from one of the end caps, then it has got warm because it is having difficulty drawing enough current. This was what was happening in my case, and I was advised to remove the fuse holder and locate the white multi-plug behind it, pull the plug apart and inspect the terminals inside. Lo and behold, after 40 years of use they had all turned a beautiful shade of GREEN! Half an hours work with a set of small jeweller's files got them all nice and clean, re-assembled and weather proofed, and no further problems!
PS. Before diving into the terminals with the files, make sure you have taken the earth lead off the battery! Regards, Mick.
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How many fuses are there 1 or 3(not counting spares)
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3 Bryan. The 15a, and 2 x 7a
The 15 is the main and the 2 7A are for the Headlight and Tail light.
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Does it blow with the other fuses (7A) removed?
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Disconnect ignition switch and see if it blows then
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Gents
Many thanks for all your kind replies - to answer
Disconnect ignition switch - Fuse only blows when ignition turned on.
Blow with other uses removed? - Don't know, haven't tried, but other as fuses are a separate circuit, i imagine it would
Switchgear wiring - My prime suspect, but I did disconnect all of it and the lamp still lit across the fuse terminals. I'll try it again though...
3 fuses 2 x7A 1 X15A
Fuse holder etc - yes , i'll take a look at it. Could be short behind it/on it.
My basic plan is to place the tail lamp across the fuse terminal, ignition on, and just go through stuff until it goes out - or dims considerably. Bike all worked fine before disassembly, so I am thinking it can only be electrical stuff that I have touched! Switchgear mainly.....
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Hi Mark,
Your bike is a US import which would once have had daytime running lights at the front with twin filament indicators. Have those wires from that system got mixed up with some others, especially earths? Can’t remember the colours of those though.
Ian
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Gents
Back to basics I feel, and in order to substatiate my thinking - or not as the case may be!
Why does a 35A fuse blow when ignition is on! Not getting that at all. There is nothing in that fuse circuit pulling that much amps just when ignition is on and nothing energised - like starter or some such.? If there is a short somewhere, then it surely would not blow a 35A fuse?
Is my theory of the tail lamp being brighly lit when ignition is on a true indication of a short? If ignition is on, there would be power across the fuse anyways...
Deeply confused....
Ian - Hello! I knew I shouldn't have fiddled! I'll check all the wiring in the shell - again - but it was all labelled up and went back the same way. headlamp and the wiring connector are currently off the bike...
Incidentally, when ignition tereminal connector is pulled, light goes out - which to me is hardly surprising as I am thinking the ignition swtich is the feed latch for the fuse. Does this indicate anything else though?
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Somewhere a wrong wire is connected to a black wire OR a black wire is trapped.
To sort this you need to be VERY methodical.
Disconnect everything yes i mean EVERYTHING Take mutimeter set on low ohms and check reading when leads connected together, treat this as zero. Connect the black lead to a good earth and start testing with red lead first to all red points then turn ignition on and all black points.
Report back as full procedure to much to assimilate in one go.
You should be seeing infinite resistance(super high)
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Hello again,
Brian confirmed the colours earlier for the daytime stuff, one blue, one orange both with white tracers. Can you see those in the bunch? - they should not be connected to anything! I think they are both female which means that if the sleeves are intact, they should be safe left alone. BTW If you put a 35 amp fuse directly across the battery it WILL blow.
As you turn on the ignition, under US circumstances, the daytimes will light - if either (or both) of those is earthed, they will produce a direct short and blow any fuse.
Pictures of the bunch might help and as Bryan says check for trapping. Did you have the loom completely off from the headstock?
Ian
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A question for those of you with USA bikes with the daytime light, does the tail light come on and stay on with that set up?
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Yes it should but via a different circuit, not if UK RH switch has been fitted(lights on/off switch)
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Bryan - sounds like a plan. Many thanks. Pardon my ignorance, but if I follow your plan, how would I detect a short on the meter? Would it be the same effective zero reading as when the two leads touch?
Incidentally, would the in built continuity tester (which beeps) on continuity do a similar thing. It may be easier to use. In other words, it would beep if the red probe detects a short .
What do you mean by Red/black points? All connnections red or black?
Many thanks again...
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Take the fuse that blows out.
On the DC volts scale, measure both sides of the fuse holder. One side should read 12v (ish), the other side should read 0V. That's the dead side
On the lowest ohms range, measure between the fuse holder dead side and battery negative.
I suspect you've got a low resistance. It shouldn't be.
If you've got a low resistance, then it's a case of unplugging things and checking if that low resistance fault clears.
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Dont trust beep, resistance can alter it. Yes a short would be same as touching leads together, you may find different resistances which can lead to an answer. Yes red/black points is every point(connector) you can find e.g. red at both sides fuse(need good fuse fitted for tests but no battery), rectifier connector, in headlamp then same for black not forgeting all the block connectors. Should have said reconnect ign switch and turn on before checking blacks
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Something I can actually contribute to! Not sure if it will be helpful, though...
A question for those of you with USA bikes with the daytime light, does the tail light come on and stay on with that set up?
Yes it should but via a different circuit, not if UK RH switch has been fitted(lights on/off switch)
Brian has it right regarding the USA tail light.
Hi Mark,
Your bike is a US import which would once have had daytime running lights at the front with twin filament indicators. Have those wires from that system got mixed up with some others, especially earths? Can’t remember the colours of those though.
Ian
Light blue/white and orange/white IIRC
Something to file away during this process, just in case - Ian is, in theory, correct about the colors, but some USA bikes don't "fully" adhere to those wire color rules - some use black wires for the front turn signals and running lights with small colored bands at each end: plain blue and plain orange for right and left turn signals, and blue/white and orange/white for right and left running lights. For example, the attached pic shows the wiring from my '77 - the top three black wires show the blue/white, orange/white and plain orange bands. You can see how the banded black wires, which lead to the fixtures, connect to the proper colored wires in the harness...
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Oggers, as already said, you’ve got to be methodical, and to do this, really need the correct wiring diagram. Yep they can be daunting, but with a beer and a few mins become easier... just think of it as water flowing through pipes and taps (switches!)
Thoughts: and bearing in mind I only have access to a UK Wiring Diagram (attached)
(1) DON’T put a 35A fuse into a 15A rated Circuit. By doing this you are potentially overloading the wiring loom which has a design limit (30A I think?) meaning that you’ll just exacerbate your problems and may melt the loom unnecessarily.
(2) From your diagram note which services the two 7A fuses cover... on the UK bikes it’s (1) the Parking Lamp + speedo / tachometer illuminations and (2) the HI/LO beam supplies. (They are downstream of / supplied by the main 15A fuse). IF neither of the 7A fuses blow at ignition ON you can probably assume these services are not the culprit as the 7A fuses would blow long before the main 15A fuse. This may save you a bit of time.
(3) Basically, the RED from the battery goes via the 15A fuse to your ignition switch. At IGN ON it becomes connected to the BLACK.... which sends power to the various components - easily seen in the wiring diagram. Given what you describe, one of these components is shorting to ground via a misconnection ... or trapped, damaged insulation etc.
(NOTE that you should NEVER see a BLACK - GREEN bullet connection as dark GREEN is always Earth (ground) wires on the old Hondas.
(4) Try disconnecting ALL the BLACK bullets shown downstream of the ignition switch - circled in red on my UK diagram. This will cut power to:
(a) the Neutral / Oil Pressure switches
(b) the Lighting circuit supply (although discussed & ultimately on 7A circuits)
(c) the kill switch supply
(d) the starter motor solenoid
(e) the rear brake switch
(f) the front brake switch.
* ensure all these loose disconnected Black bullets (from the IGN Switch) cannot touch / short any other wires. (If your loom is original you should be ok here as they will be the Female connector with enclosed plastic sleeve)
(5) Now, with a 15A fuse try the ignition ON... if all ok then a fault lies in one of the above circuits.... connect them one at a time to single out the culprit.
(6) If the fuse blows again, the problem lies elsewhere in your circuit / loom. Note from the wiring diagram that there are a couple of ‘hard’ connections... eg the Regulator & Winker Relay. Disconnect these... and turn the IGN ON... if the fuse stays good then your fault lies in one of these...
(7) If after all the above the fuse is still blowing it’s beginning to point to a problem with perhaps the IGN switch itself... or the loom; bad insulation etc. Hope it doesn’t get to this...
Finally, whilst the UK Wiring Diagram is probably pretty accurate, it will have differences and you really need to source the correct one for your bike. Mattsz?
Good luck, ‘tis all a pain to be sure.
Simon
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Just a thought as I noticed this the other day ..
Have you had the rear taillight disconnected
It has 2 green wires and on my bike one has the faintest of yellow trace marks....almost invisible especially in a darker garage . One is an earth the other a switch on to
the lamp
I'm assuming this would run to the headlight ....if connected wrong...or together thay would cause this fault
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Finally, whilst the UK Wiring Diagram is probably pretty accurate, it will have differences and you really need to source the correct one for your bike. Mattsz?
Here's my original post:
http://www.sohc.co.uk/index.php/topic,17969.msg156361.html#msg156361 (http://www.sohc.co.uk/index.php/topic,17969.msg156361.html#msg156361)
You'll find both UK and USA diagrams as attachments, plus a dropbox link to the USA diagram at the bottom. As most of you know, they're very similar, with the exception of the running lights and headlight switch.
Also, here's a dropbox link to a pdf collection of "detail" diagrams which may help - too much time sheltering at home maybe?
https://www.dropbox.com/s/i05w722o7fxjovh/Honda%20CB400F%20USA%20wiring%20diagrams.pdf?dl=0 (https://www.dropbox.com/s/i05w722o7fxjovh/Honda%20CB400F%20USA%20wiring%20diagrams.pdf?dl=0)
This link may die sometime in the future, but I'll leave the file there for now...
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Gents
Again this is all very useful stuff and most helpful to an electrical dunce such as me!
Essentially though, I have followed Bryan's advice in so far as disconnecting stuff and testing red and black connections
Somewhere a wrong wire is connected to a black wire OR a black wire is trapped.
To sort this you need to be VERY methodical.
Disconnect everything yes i mean EVERYTHING Take mutimeter set on low ohms and check reading when leads connected together, treat this as zero. Connect the black lead to a good earth and start testing with red lead first to all red points then turn ignition on and all black points.
Report back as full procedure to much to assimilate in one go.
You should be seeing infinite resistance(super high)
Came across something in so doing...The black wire multiconnector at the headstock. The male connectors are off and read high resistance, but the female connectors seem to be grounding. Resistance is more or less zero ohms and the continuity tester beeps. Looking at the wiring diagram, one goes back to the ignition switch - which is connected by the way.
Could this be the culprit and if so - how to test the switch please?
As an aside, when testing between the dead side of the fuse holder and earth/ground, the reading fluctuates from very high to zero ohms - which seems odd....
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The ignition switch switches 12V to the loom, or to the side light. It doesn't switch 0V, You can disregard the switch shorting to 0V, but it looks like you're on the right track.
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Right - ignore my last. Wrong black lead identified as the culprit, though the connector was right. So, to confirm, the suspect connection is the 5 point BLACK multi-connector at the headstock. All wires were discinnected except the common and by that I mean the middle RH wire on Lobo's diagram. That is the one which still grounds. Therefore black probe of the multimeter on this connector/wire, and off with the black connectors for the stop switches - still grounds, off with winker relay black connector - still grounds, then off with the regulator black connector - and lo! no ground! Tested the black terminal of the regulator and it grounds. I assume it should not, and I have therefore found my true culprit!
Where now!
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.and actually all 3 terminals on the regulator ground. I guess the green one should, but not the other two?
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If the contacts in the reg box are closed the black conects to white which goes to the field coil then groung.
Disconnect the multi plug to the engine reconnect the reg and see if the black still grounds
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Bryan - Wilco - just to clarify, which multiplug are we talking about here? Refer to Lobo's colour wiring diagram if you must!
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I'm on the edge of my seat with this episode of 'Honda Wiring Problems Diagnostics'. It makes for far better watching than any of the crap on TV 😊😊😊😊😊
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The one on the end of the engine lead 3xyellow, 1xwhite,1xgreen,1xlightgreen/red, 1xblue/red 7 leads in a 9 pin plug on electric panel.
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Julie, at least this poster is listening, unlike some of our US friends enen on wing board
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Julie, at least this poster is listening, unlike some of our US friends enen on wing board
That's true Bryan. You are an excellent Tutor Bryan and I'm pleased I pointed Oggers in the right direction from the USA site to here.... 😊😊😊😊
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Ok - disconnected the 9 pin plug connector. Same result.
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Does the main loom plug into the electrical panel on a multi block? If so disconnect there and try black in loom again.
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Lost me again I'm afraid! Main loom??? Electrical panel? Wiring is essentially as per Lobo' s diagram. I can follow that!
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That diagram is a schematic not literal.
Main loom is the big bunch of wiring along the bike front to back. Main panel is where the regulator, rectifier, flasher relay and solenoid are fixed.
I will look in my garage and see if i have a 550 one spare to look at, mostly i have 500 so not sure.
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Ok understood. Rectifier has multiplug connector, regulator has 3 spade connectors - white black green, flasher relay two spade connectors, solenoid as per wiring diagram. No large connector to main loom that I can see.
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That diagram is a schematic not literal.
Main loom is the big bunch of wiring along the bike front to back. Main panel is where the regulator, rectifier, flasher relay and solenoid are fixed.
I will look in my garage and see if i have a 550 one spare to look at, mostly i have 500 so not sure.
It's a 400 Bryan.
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Forgive my presumption here, but surely that black connector and wire to the regulator must not be grounded. If so, it would provide a clear short path for the hot/feed wire direct from the ignition key, and surely blow the 15A fuse?
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Any black wire, treat as 12V and deffo not to be earthed. All earth wires are green. Not green/yellow - green
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Oggers, within the Regulator the Black is connected to Green- via a winding (in red on the attached diagram). My point is, depending on how you are using your multimeter, you might be wrongly assuming a false earth on the Black. Don’t use the beeper between Black and Green (my two blue marks), but rather the Ohm scale. Compare what you see with directly putting the two probes together... which would signify a true earth fault.
Sorry... but can’t tell you an expected Ohm reading between the Black and Green terminals, but it won’t be 0 (pure short) and it won’t be infinity (open circuit).
It’ll be great indeed if the Black on the regulator is definitely shorting to ground....
Simon
PS Have you tried a 15A fuse back in the circuit with the Regulator disconnected to confirm if it’s the culprit... this might be the easiest way.
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Ooops, forgot that. Is there not a sub loom on the 400 Julie, its been a lot of years since i did electrics on one of those. All basically same just slight variations
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Oggers... just put an Ohm meter across the Black & Green of my 400F Rectifier (and disconnected from the loom).... saw 108 ohms.
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Quick look at parts list tells me no sub loom so if the black goes to ground only when connected to regulator has to be regulator fault, if goes to ground when not connected loom has a problem or wire trapped/connected wrongly somewhere
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Chaps
To confirm various things
Two multimeter probes crossed gives a reading of 0 Ohms
Test 1
Red probe to the single common BLACK wire at the headstock multi-connector. Everything else on this common disconnected except to the regulator
Black probe to earth/ground
Result - Resistance of 0 Ohms - Short?
Test 2
As above, but with regulator black wire disconnected
Result - Infinite Ohms - No short?
Test 3
Red probe on green regulator terminal
Black probe on black regulator terminal
All wires disconnected
Result - 0 ohms - short inside regulator?
Overall result - duff regualtor?
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...I’d reckon job done; and indeed it seems the Regulator has gone bad describing the 3 checks you did.
The last bit of your puzzle will be confirmation with a 15A fuse in place... but Regulator disconnected of course.
Seems an odd sort of failure... has the Regulator Black contact somehow bent / contacted the body?
Regardless, hopefully well done.
Simon
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The proper 400 reg has contacts that poinr sideways whilst the other fours point downwards perhaps the wrong one fitted
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Simon/Bryan
Firstly many thanks to you both. Would not have found it without you.
Yes - for sure I will reconnect everything except the regulator, insert fuse, turn the key and see what happens. It had better not blow!
I'll pull the regulator off to see if I can find anything obvious, but yes, a little odd for sure. I never touched it! Some elderly capacitors in there, so I guess they have a shelf life.....
Pins point outwards by the by
May invest in the reg/rec combo as a fix....
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No capacitors, all coils n points.
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Have you stopped the blowing fuses?
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Bryan - not quite 100% rewired just yet - further problems!, but so far, 15A fuse back in, disconnected from regulator and no blown fuse.
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Glad you've traced the fault. With so many things connected to the positive, it can take a while to eliminate the fault. Time is something we have oodles of at the mo.
Is you reg the original metal can one or is it a more up to date reg/rec ?
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Mike
Its the old seperate type. Lord knows why it seems to have just stopped functioning. Took it apart, cannot see anything obviously amiss. Ordered up replacement.
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a year or so ago on a german website i came across a person/company? who were advertising a modern rec/reg unit that was housed in the original "can" type unit. has any other member come across this item?
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Most people go for the combined reg/rec. You'll need to alter the wiring slightly, and you could leave the faulty one in place.