Author Topic: Blown fuses  (Read 2527 times)

Offline Orcade-Ian

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Re: Blown fuses
« Reply #15 on: April 04, 2020, 03:57:14 PM »
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


Offline Nurse Julie

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Re: Blown fuses
« Reply #16 on: April 04, 2020, 04:19:40 PM »
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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Offline Bryanj

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Re: Blown fuses
« Reply #17 on: April 04, 2020, 04:25:35 PM »
Yes it should but via a different circuit, not if UK RH switch has been fitted(lights on/off switch)

Offline Oggers

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Re: Blown fuses
« Reply #18 on: April 04, 2020, 05:23:54 PM »
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...


Offline mike the bike

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Re: Blown fuses
« Reply #19 on: April 04, 2020, 06:41:53 PM »
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.
Where's that 10mm socket got to?

Offline Bryanj

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Re: Blown fuses
« Reply #20 on: April 04, 2020, 06:50:09 PM »
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

Offline mattsz

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Re: Blown fuses
« Reply #21 on: April 05, 2020, 01:41:05 AM »
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...
« Last Edit: April 05, 2020, 01:43:57 AM by mattsz »

Offline Lobo

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Re: Blown fuses
« Reply #22 on: April 05, 2020, 03:44:29 AM »
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
« Last Edit: April 05, 2020, 04:36:26 AM by Lobo »

Offline Woodside

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Re: Blown fuses
« Reply #23 on: April 05, 2020, 08:32:53 AM »
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

Offline mattsz

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Re: Blown fuses
« Reply #24 on: April 05, 2020, 10:09:49 AM »
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

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

This link may die sometime in the future, but I'll leave the file there for now...

Offline Oggers

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Re: Blown fuses
« Reply #25 on: April 05, 2020, 01:42:27 PM »
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.... 

   



Offline mike the bike

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Re: Blown fuses
« Reply #26 on: April 05, 2020, 05:24:11 PM »
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.
Where's that 10mm socket got to?

Offline Oggers

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Re: Blown fuses
« Reply #27 on: April 05, 2020, 05:51:20 PM »
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! 

Offline Oggers

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Re: Blown fuses
« Reply #28 on: April 05, 2020, 06:04:20 PM »
.and actually all 3 terminals on the regulator ground. I guess the green one should, but not the other two?

Offline Bryanj

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Re: Blown fuses
« Reply #29 on: April 05, 2020, 06:28:16 PM »
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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