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R75/5 Horn won"t work

Of course, check all wiring.

If you have a 12V test light, disconnect wire to horn, and insert light - other end grounded. Then turn on ignition, push horn button, if you have light at the tester, then the horn is the culprit.

May need cleaning and re-adjusting to get vibration going, or just may need replacing.

Second: if horn is ok, check the horn relay (on my /7 it is under the tank on the frame). Often these get dirty and clogged up inside. Thought they are not meant to be repaired, you can do some.

Pry off the cover carefully (usually cover is aluminum, and has tabs that can be bent) and look inside.

Clean out completely. Check the contact and test the relay before putting back on the cover. I put mine in the bike, and then pushed horn button and watched how the relay "clicked" to make the horn connection. I thoroughly cleaned, then coated some with di-electric grease, reassembled, and it still works.

Saved me about $35.00.

Horn button would be the next logical thing to check - is it making contact?
 
On a /5, you have two connectors. One has two wires crimped into it. This wire (green with black stripe?) is hot whenever ignition is on. The other one runs to the horn button. So you need to check for 12V at the double wire connector and ground at the other connecter when the horn button is pushed. If that's good, you can hook a battery directly to the horn to see if it works. Did it ever work? The contacts in the button can get corrosion on them, too.
 
My fuse block inside headlight bucket had melted & horn wires weren't connected to block - RX was new fuse block, connecting horn wires & replacing 40 year old control wires on handlebar with broken connections under horn button.
 
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