Tech Forums > SOHC/4 Bikes
Horn repair, doesn't work below 3000 RPM with headlight on
Dunk:
My horn was not working consistently, or below 3000 RPM wasn't working at all with the headlight on. I figured it was because I ride this bike daily year round so it sees plenty of rain, occasional snow, and salty roads.
First I cleaned all electrical connections at battery, grounds, main harness. Added silicon grease to the open big connectors, seems like a good idea. Checked voltage at idle headlight off and on. Not good, slowly dropping below 12v. At 5000 RPM it's around 14.7v after giving it a few seconds to get there. Battery is an AGM at least a few years old, probably not helping matters. Solid state voltage regulator that's adjustable, but did not adjust it since it seems about where it should be at RPM.
So I removed the horn and heard rattling, rotated it a few times and some small gravel came out. I opened it up and found a bunch more that surely wasn't helping things. Cleaned the points with fine sandpaper, reassembled. It works better, now around 1400 RPM with headlight on but still flakey presumably due to low voltage. Will adjusting the screw help it work better at lower voltage?
Not looking forward to winter, heated gloves and such with such a marginal alternator.
scottly:
--- Quote from: Dunk on August 24, 2025, 01:00:50 PM --- Checked voltage at idle headlight off and on. Not good, slowly dropping below 12v.
--- End quote ---
The battery voltage with the headlight off drops below 12v?? The problem is with your charging system, not your horn. Check the voltage drop from the battery plus terminal to the black regulator terminal, with the key on, engine not running. The voltage should be less than 1v.
Deltarider:
Heated gloves? Really? How much do they draw?
Deltarider:
--- Quote from: scottly on August 24, 2025, 08:10:59 PM ---
--- Quote from: Dunk on August 24, 2025, 01:00:50 PM --- Checked voltage at idle headlight off and on. Not good, slowly dropping below 12v.
--- End quote ---
The battery voltage with the headlight off drops below 12v?? The problem is with your charging system, not your horn. Check the voltage drop from the battery plus terminal to the black regulator terminal, with the key on, engine not running. The voltage should be less than 1v.
--- End quote ---
Although I have never done this test, I have the gut feeling this is best done with a battery charger max. 1A connected to the battery. Is my gut feeling right? Kill switch better be off. Please report back.
HondaMan:
Your 'heated gloves' comment spooks me: the CB550 only makes 1A 'extra' power (when new) when the lights are on (and the engine is turning 4000+ RPM). Your gloves probably pull several more amps than that.
This particular electrical system was designed before the USA suddenly demanded that all motorcycles sold here had to ride with the lights on all the time.
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