Sounds more like a voltage drop either across the switch or in the wiring to the horn. Most likely in the wiring especially if it's in the head lamp housing and like the other guy who has a problem but not at a higher rpm it's most definitely drop in the wire.

 

What you did was to let the horn switch control the relay rather than causing the switch to carry the load of the horn. The wiring can carry enough current to operate the relay but was marginal to operate the horn.

Good short term fix but you may see problems down road, then again I have seen that fix last a long time too. You can have 12 v at certain point in a circuit but not enough current flow (amps) to operate a given component.

WP

 

Guy's this chicken sheite horn problem is why relay's are used,A relay makes it possible for a accessory such as a horn or a fuel pump to get a full shot of juice from the battery.On the battery power circuit from the relay use the heavy wire and for the ground side go right to the negative terminal of the battery and coat all the connections with a light coating of grease. The Harley horn circuit with the small wiring and the light duty handlebar switch signals the relay.I learned about relays from owning a Porsche 911.Everything is premium on the 911 including every circuit in the car using a relay and heavy gauge automotive wire.

 

I'll agree except that to many relays cause their own set problems. Just another set of contacts and connections to become weak and add resistance to a circuit. Have been an auto mechanic (tech as we are called today) for 30 + years and 24 of those at a Cadillac dealer. GM has put out some real junk as have most any auto manufacture has at one time or another including a few Porsche's I have dealt with.

WP