1976 R75/6 horn button dissesction

[Dworth99]

Hi fellow riders. the horn button on my 1976 R75/6 doesn't seem to complete connection when I push it. Horn tested good and I have 12v on the hot side of wire to horn and continuity on the ground wire (brown/white) all the way back to the switch. Has anyone tried to take this switch apart? A closeup of the switch shows what looks like a brass pin at the bottom holding the switch cluster in place. I removed the yellow light toggle but that did nothing to allow the rest of the switch to be removed from the housing. Any help is appreciated!

[gspd]

Have you established that the solid brown wire at the switch is solid ground?
Jumping the brown/white wire to the brown wire should activate the horn.
The horn switch is just 2 simple contacts and rarely fails in a way that a squirt of contact cleaner won't fix it.

To take the switch apart you have to remove the circlip and pull out the (yellow) switch, then pry the whole assembly out of the outer housing. I would suggest doing this on a white sheet, as there is a tiny spring and ball that will pop out with it.
Haven't done this in decades, but I recall it being quite simple as long as no small parts are lost

[Dworth99]

Thanks gspd for feedback. I've dug into this horn issue farther and found the horn button does work. Traced wiring for corrosion at connections and cleaned them. while testing things out I found I am getting 9v at the green/black wire (+) connecting to the horn (brown/yellow wire connects to negative post on horn) when the ignition is off and when turned to parking but get 0.14 v when the ignition is turned to start. In addition, the dash lights flash when pressing the horn button in both ignition off and parking mode but dash stays lighted when in start mode. Blinkers, lights, stop lights all work fine and engine starts and runs just fine. Looking at Brooks wiring diagrams for R75/6, I don't see how I should measure 9v at the (+) horn wire when the ignition is off even with the kill switch is toggled to off. Wondering if I have and ignition switch problem despite everything else working. Anyone seen this before?

[gspd]

I find troubleshooting these old bikes simpler and quicker with an old fashioned incandescent (not LED) test light than with a digital voltmeter. An old style test light creates a load when testing a circuit, a DVM does not. If you don’t have one handy, make one up with one of your flasher bulbs; an alligator clip to battery negative on one end and a pointy probe/pin to poke through wire insulation on the other.
You will be able to tell by the intensity of the light if the circuit is working properly.

Basically, every circuit you test should light up the test bulb as brightly as if the test light were connected directly to the battery positive and negative. The test light will be noticeably dimmer anywhere you have a dirty or loose connector along the line.

Your bike is 50 years old. Start by disconnecting and checking every possible connector that you can find for corrosion or looseness. Look for chafed wires, dirty grounds, etc. Pull out and check all relay connectors, all grounding points, etc. To check ground circuits, same procedure but with the alligator clip attached to the battery positive.

In over 50 years of working on these bikes I've never had one I couldn't fix, I'm just not a great teacher.
For me this stuff is very easy to do in person but I’m not great at explaining it in writing.
Rob F is the man for that.

[Dworth99]

GSPD was exactly right. I went back into the headlight shell and found the ground wire came loose from the wiring circuit board and had come into contact with the positive block on the circuit board. As a result, i was getting these strange voltage readings at the horn wires. Once the ground was placed back in the correct place on the circuit board, no more issues and horn worked perfectly. Thanks again GSPD.

[SteveD]

...
In over 50 years of working on these bikes I've never had one I couldn't fix, I'm just not a great teacher.
For me this stuff is very easy to do in person but I’m not great at explaining it in writing.

You do awright GSPD.