Topic: Trying to track down my horn electrical problems...

[Dave-and-his-550]

Hey guys, been awhile since I've posted on here. I'm going to be taking my riding skills test on Monday, and I need to get my horn working this weekend. The wiring diagram hasn't really helped me in figuring out what to check next.  But what I do know, is that the horn itself is good, checked it with the battery. I checked the black wire in the harness under the tank that hooks directly to the horn with a test light, and it lights up. So I got power there, but I'm not sure where to check next.

I read that the horn is grounded via the horn button, so I was about to go open that thing up and check if its in good condition. Is that the next step? Checking to see if the ground is good at the switch? Or should I check elsewhere first, like the headlight bucket wiring?

In the mean time, I'll go sifting through any old threads I can find on horn issues.

Bikes a '76 550F by the way. Thanks for any help!

[Steel CB650C]

Hi Dave

I think your on the right track I would check the switch next.

[Dave-and-his-550]

Okay, I unscrewed the horn switch and looked inside, I tried to unscrew the little screw holding the wiring to the horn switch in, but it wont budge at all, and I dont want to strip it out quite yet. The ground at the horn switch is the end of the circuit am I correct? If so, shouldn't I be checking some other wiring first before I check the switch? I know the wiring to the horn itself is good, so whats next "in line" from the wiring to the horn? Perhaps in the headlight bucket...Does the wiring to the horn run through there before it connects to the horn switch?

[bryanj]

Right before you go any farther is there 1 or 2 wires going to the switch? the later bikes/switches have 2 wires (black and light blue) and on these they power the horn which needs to be grounded to the frame with a loop wire, not fed from the loom.

Down and dirty test is check for 12 volt between wire from switch at horn and a good ground, if yes fit a grounding loop between other horn contact and a mounting bolt

[Frostyboy]

Right before you go any farther is there 1 or 2 wires going to the switch? the later bikes/switches have 2 wires (black and light blue) and on these they power the horn which needs to be grounded to the frame with a loop wire, not fed from the loom.

Down and dirty test is check for 12 volt between wire from switch at horn and a good ground, if yes fit a grounding loop between other horn contact and a mounting bolt

+1 Bryan. Mine is a '76F and unlike a K, the horn is powered via the switch & grounded to the frame.
The power source is light green though, not blue.

[Edit] This wiring diagram suits my bike, it may vary according to what country your bike was destined for.

[bryanj]

Frosty is right about the colour i was working from memory not a switch!!

[Frostyboy]

Frosty is right about the colour i was working from memory not a switch!!

You did good anyway Bryan. Must be a lot in that memory bank. The light green could certainly look blue in the right light anyway. 

[Dave-and-his-550]

Well there appears to be just one green wire going to the horn switch. My horn has two wires feeding from it, that both seem to attach to the harness wires. There is no indication that the horn ground wire bolts to the frame at all...?

Also: When I hook the horn up to the live wire from the harness, and touch the ground wire to the bike, the horn sounds.

[Dave-and-his-550]

Okay here is what I've tested so far: I checked the harness wires (green and black) with a voltmeter and got nothing. I then checked the black wire from the same spot and grounded it to the frame and got a reading. I then checked that black (harness) wire to the green wire at the switch and got the same reading. I used the ohm meter on the black and green at the harness and got nothing. Then did the black wire and bike ground and got a reading. Same with the black and switch green wire. So...that green wire at the harness seems to be my problem, correct?

"Connect the black to horn and turn on the keyswitch.  If you frame ground the open terminal, the horn should sound." <--I did this and the horn works.

[Dave-and-his-550]

Okay here is what I've tested so far: I checked the harness wires (green and black) with a voltmeter and got nothing.

With the keyswitch on or off?  With this reading I hope the Key switch was off.

^^This was with the keyswitch on.

I then checked the black wire from the same spot and grounded it to the frame and got a reading.

What?!   The black wire carries 12V when the key switch is on.  Connected that to frame, and you'll be replacing fuses.  Connect to frame via the Voltmeter and you should get 12V (provided key switch is on).

^^ Here I meant I connected the voltmeter to the black, and the voltmeter ground wire to the frame. Sorry for any confusion!

I then checked that black (harness) wire to the green wire at the switch and got the same reading. I used the ohm meter on the black and green at the harness and got nothing. Then did the black wire and bike ground and got a reading. Same with the black and switch green wire. So...that green wire at the harness seems to be my problem, correct?

The test technique is a bit of flail and not really definitive.  But, I think your conclusion is correct.

^^ I'm thinking my horn switch is good but I'm still not sure if I tested it correctly. It really seems like that one light green wire at the harness has issues, because like I said, I hooked black and green wires there up to voltmeter and got no reading.

Honestly, I'm not sure how to use the ohm setting on my tester 

[Frostyboy]

Like I said in my earlier post, & can be seen on the wiring diagram there, the light green is 12v supply from switch & the black is connected straight to ground.
I'm beginning to wonder if you have the correct L/H control on that bike?
Another subtle difference that I've referred to in other posts, is that the starter on my F is powered from the button - not grounded by the button. The horn & starter do seem to cause some dramas when swapping controls from one model to another.

[Dave-and-his-550]

I think my voltmeter battery is bad probably, because the screen goes completely blank when I test with the Ohm settings I hooked up the red test wire to the LG at the frame, and the black test wire to the frame ground, and the screen goes from reading -1 to completely blank...?

I'm beginning to wonder if you have the correct L/H control on that bike?

Yeah, I'm wondering this also. You said the 550F's had a LG and black wire in the horn switch, and the horn was grounded to the frame with a loop wire...My switch only has one LG wire. And the horn has two wires that plug into the harness wires 

[Frostyboy]

Frosty,
I think you may have an export model/schematic. 
Check the Honda Cb500/550 Shop manual schematic for USA distribution (Chapter 16 supplement).  The button grounds to bars and 12 V runs to the horn for US models.

The F2 Schematics in Chapter 20 show your presented wire connection scheme for General type, U.K. European Type, French Type, and Germany Type.  The USA and Canada type horn button grounds to bars.

Cheers,

Agreed TT. That scematic is suitable to my machine however.

[Dave-and-his-550]

Well, the way its looking, I get no reading from the LG wire at the harness. And that is with the voltmeter hooked up to the LG and Black at the harness, pushing the horn button. So...that means my horn switch is bad? It all seems to be connected together fine.

[Frostyboy]

Apologies for leading you astray with details for the wrong machine. I'll never quite understand why there needs to be such differences in models for different countries.
All the same, if you have 12v at the black wire to the horn simply ground the light green wire up near the control somewhere.  Maybe the switch is bad after all.
Just in case, have you checked to see if the bars are actually connected to ground properly?

[Dave-and-his-550]

Just in case, have you checked to see if the bars are actually connected to ground properly?

No I have not, how do I check this?

[bryanj]

You need a working ohm meter to test the horn button, not a voltmeter, and check resistance bewtween light green at horn and bars with button pushed--it should be zero and with button unpushed infinitely large

[Dave-and-his-550]

Sorry, what I meant to say was multimeter.

The setting I have on my multimeter for checking resistance has Ω on it, and on that it goes from 200-2000k. I have it set on the 200Ω setting. I hope thats right.

It probably matters if I connect the ground lead of my multimeter to the horn switch plate or the horn switch wiring (The solder bead over it rather). Because this is what I've found out:

With the multimeter red lead on the black harness wire, and the black lead on the horn switch plate, I got a reading of 2.0-3.0 (fluctuated a little) with the horn pushed and not pushed.

But, when I have the red lead on the black harness wire, and the black lead on the horn switch wire itself, I got no reading, horn pushed and not pushed.

Just so I understand this right, this is how the wiring of the whole thing goes:

Horn wires to the harness wires -> black harness wire to power -> green harness wire to horn switch button. Right?

If I'm getting no reading at all at the horn switch wire, I guess I should try and unscrew it because it is quite corroded, and that is probably the obvious problem.

What of my multimeter results though, indicates the switch is bad?

[bryanj]

If you had the reading set to Ohm and put a lead to black(power) you have blown your meter mate, they are not designed to have voltage applied when set to reistance reading

[Frostyboy]

Dave, forget about the black wire to your l/h control, it doesn't work the horn.
Check that you have battery voltage at the black wire at the horn itself. Check it with voltmeter or a test light.
What works the horn is when the light green wire is taken to ground. Follow the lg wire to the harness connector under the tank. Seperate the connection & simply touch the wire to the frame or anywhere on the engine. Does the horn work now? If so, the problem lies ahead.
Now set your meter to ohms, connect it to the end of the wire going towards the switch. Connect the other wire on your meter to your handle bar. With the button pushed, there should be 0 ohms.
If open/ol the switch is not working.
As far as checking if the bars are grounded, now that I think about it, if the start button is working then the bars are grounded so that's not an issue.

If you had the reading set to Ohm and put a lead to black(power) you have blown your meter mate, they are not designed to have voltage applied when set to reistance reading

Like Bryan said, test your meter by touching both probes together on ohms setting. Result should be 0. If o/l you've blown a fuse inside or worse. Is it a digital meter?

[bryanj]

Frosty just cos the starter works don't mean the bars are grounded---dont forget the later bikes had the headlight on all the time and the 3 wire starter button that powers the solenoid not ground it

[Dave-and-his-550]

Now set your meter to ohms, connect it to the end of the wire going towards the switch. Connect the other wire on your meter to your handle bar. With the button pushed, there should be 0 ohms.
If open/ol the switch is not working.

Yea it is not reading 0 ohms. I get the open/ol message.

Like Bryan said, test your meter by touching both probes together on ohms setting. Result should be 0. If o/l you've blown a fuse inside or worse. Is it a digital meter?

My multimeter works fine I tested it, and yes its digital!

Considering I'm not getting a reading when I have the horn switch wire tested like how you said, it looks like its bad. So now I guess I'll try and uncrew that wiring, take out the little parts and clean them up real good. What was that grease thats good for corrosion protection? Dielectric grease right?

And sorry about testing the wrong things earlier, I realize now I was doing a lot of unnecessary things. I have not done any real electric troubleshooting before. Just yesterday I figured out how to do continuity testing with my multimeter. Apologies go out to TwoTired especially 

[Dave-and-his-550]

Just an update. I had to do some cutting of those little screws holding the wiring in, finally got them off and I wanted to post pictures of the horn switch condition. I guess what I will do now is clean up the contacts with a fine file, try and de-rust whatever I can. Let me know if you don't see any of the images.

In that first picture, can I pull out that wiring from its little harness? Does it pry apart? (I'm afraid to break the wire if I try and force anything)

[Dave-and-his-550]

Cleaned everything up and screwed it all back together nice and tight. The horn works just great now. Thanks for all the help! Turns out all it needed was a lot of cleaning at the horn switch contacts. 

[Frostyboy]

Leslie RS5T train horns on motorcycle, Really Loud :0