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Motorcycle Repair/1975 honda cb360t horn

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Question
Hi Bill,

Just bought a 1975 Honda CB 360t.
Got it running after changing the spark plugs, new fuel, and installing a new battery.

That's about the limit of my skills at this point. It's my first bike and I'm in the process of learning.

I knew the horn was not working when I bought it. I found a used horn on eBay and installed it. (It was reportedly working when removed from donor bike).
But, it still doesn't work.

The wiring diagram looks like Greek to me.
I tried connecting directly to both horns and a third horn my dad had lying around. But none work.

Is there a common failure point for these horns or an easy way to fix it?
I have 5 days left to get it inspected.

Any help would be greatly appreciated.
Thanks,
Mike

Answer
Mike, power for the horn comes from the ignition switch goes through the horn and waits for the circuit to be connected by the horn button, which grounds the whole circuit.

If you put 12v on all three horns..  hot 12v to the terminal and ground on the other connector lug, then the problems must be in the horns themselves.  Horns really don't get used very much in real life, so the contacts inside the horn assembly can become corroded and lose their electrical connection through the contact faces.

If you look at the back side of the horns you will see a locknut and set screw, painted over with inspection paint at the factory. Loosen the nut up and turn the screw about 1/4 turn in and test the horn again. If nothing try another 1/4 turn in. Still dead, try turning it out 1/4 turn from where you started. The screw changes the point gap on the horn, which will change the pitch of the sound, when they are working.  If none of them respond to adjusting, you can play with one of them and pry it apart to see what's inside, just for your own education.

A horn is a horn, so check with eBay or a local bike parts shop/salvage yard for one that is similar to yours and have them test it before you buy, so you can pass your inspection test.

Bill Silver  

Motorcycle Repair

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Bill Silver

Expertise

Need help with vintage Hondas from the 1960s? I am an expert with 250-305cc bikes in particular and most all of the other pre-91 models, in general. I do NOT claim to have a great deal of experience on Gold Wings, Cruisers, ATC/ATVs and dirt bikes.

Experience

I have owned/ridden/maintained Honda motorcycles for 35 years. I have written five books on Honda repairs and collecting. I was a service manager for two Honda shops back in the 1980s.

Organizations
VJMC (Vintage Japanese Motorcycle Club) of North America

Publications
VJMC newsletter, as editor for two years and as contributing editor currently.

Education/Credentials
3 years auto shop in high school, teacher's aide in Automotive Technology in Jr. College, Diesel mechanic course in college, self-taught mechanic and automotive writer.

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