Honda-SOHC
SOHC.co.uk Forums => CB350/400 => Topic started by: ted_paper on January 02, 2025, 02:37:21 PM
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I have just disconnected my old horn with the intention of replacing it with a louder (hopefully) one.
When I fitted the new one - nothing. So I swopped it back for the old one - again nothing.
I didn't check before removing the old one that everything was working so that was probably my first mistake...
As I have said on a previous post, electrics are a bit of a mystery to me. I have a multimeter which I am not entirely familiar but have established that my battery is fully charged, and if I stuff the 2 probes into the connectors to the horn, switch on the ignition and press the horn button then there is no reading showing.
Any advice where to start looking would be gratefully received.
Thanks
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Does any of the switches in the left hand switch gear work?
Do you get lights and indicators?
Try and make a circuit tester,
Use a bulb holder, like fitted as the idiot lights, and get a couple of crocodile clips, that will make life much easier
Have you got a wiring diagram??
Good luck
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Yep, lights and indicators are working.
I have a Haynes manual showing the wiring, but I'm not sure how or what I should be testing... :)
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If you can find a simple tester as I said, earth one lead to the motor or bolt head on the frame,
The other wire connect to a horn lead,press the button, hopefully the bulb will light,
Do this test on both leads,
Can you make out the colour of the leads?
Do they match the manual?
Have you tested the horn??
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As John has said I would start by simply putting a test bulb where the horn was connected - if it does not light up with the ignition on & horn button depressed start checking for voltage in the circuit.
Some Hondas have the earth wire at the horn end with a live feed to the horn from the ignition circuit via the button. Other models have the button as the earth connection.
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There are two different sets of wiring depending on year and model of bike, need to know both those before answering
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You might also want to check out my 'Horn of Death' :o thread on CB400F horn wiring! ;D http://www.sohc.co.uk/index.php/topic,27401.msg254773.html#msg254773
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Bryanj - It is a '77 model with 2 wires that look to be a green and a black.
John - I thought I had a two-pronged bulb to make a simple tester - turns out I haven't so will have to get one at
Halfords! The horn(s) have been tested and they are both working.
Athames57 - Thanks for the link - I've already looked at a thread going back to 2013 which went straight over my head!
Waiting on my lamp tester now.
Thanks
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OK a 77SHOULD have one wire at the horn going to ground and the other supplying power from the switch IF everything is original which it may not be.
To be certain split the LH switch and see how many wires go to the horn button and report back.
Long distance elektrickery diagnosise takes time and patience, by the way you didnt say what 77 bike it was so i am still guessing
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Thanks for feedback.
Grandchildren visiting this weekend so garage time is curtailed until Monday :)
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Sorry if I have missed this, but what export market model is it? UK, USA, other?
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Maybe I'm not understanding something but if you have a multimeter, why obtain a test light to check for voltage at the connectors?
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It' a UK model
As to why to use a light test, I'm not familiar with the various settings on a multimeter and this might be an easier method?
Electrics are not my forte... :-\
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If you go on U tube there are quite a few videos showing you how to use a Multimeter. TBH I use mine mainly on the DC volts setting range.
None of us are born electricians, it's a relatively easy skill to develop, you don't have to be able to use all the settings on a meter just a couple of basics will help you become more confident.
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We can help with the multimeter.
Show us a photo of it and we’ll tell you what settings to use and what they should read.
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Cheers guys
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Turn the knob to the left till the arrow points to the white mark with 20 on it, if you connect the red lead to positive battery and black to negative battery it should show about 12v, you then leave the black on the battery and test for voltage at various points, still need to know what wires go to horn button to be exact and is the same button a headlamp flash as well
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Managed to sneak into garage for 10mins.
Reading is around 12v
Split L/H switch photos attached
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Pic dont help, need to know what colour wires go to horn button
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Ted,
Where are you located? There might be someone local to you who could help.
Michael
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Managed to sneak into garage for 10mins.
Reading is around 12v
Split L/H switch photos attached
Where did you take the 12v reading from?
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If there are TWO horn wires, connect the black probe to one and the red probe to the other. Turn on the ignition and press the horn button. You should see "battery voltage" (12-13V) on the multimeter. You might see - (minus) voltage but that doesn't matter in this case. It just means that you connected the red lead to the negative (earth/ground) wire instead of the hot wire. Makes no difference for this test.
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Solved!
Thanks to the advice given, I traced the problem back to the spade connectors.
When trying the probes, one to the connectors seem to "wobble " a bit more than I expected so I gave it a gentle wiggle and it come off with few millimetres of wire. Did the same with the other and the same result. I managed to remove a small piece of sleeving to reveal the wires and the bulb test worked! :)
I just need to cut back a bit more to try and extend the wires to the correct length.
The only strange thing is that both of the spade connections show signs of melting.....
Thanks for your patience and all the help given.
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I’m guessing that the poor connection created a high resistance joint resulting in the production of excessive heat, which is unusual given the normal type of horn use. Oddly enough my horn connections show similar signs of heat distortion, but not to that extent.
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Proximity to a hot engine/exhaust pipes doesn't help.
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Aye, certainly a possibility if not a probability.