its normal .
the horn is designed to work without a key . .. always at the ready .
so it is normal and correct ... ( for stock wiring ) ... for most 60s britbikes .
it's how it was done back then as a safety feature . ..
the load is way too much for any Lucas
key switch .
and bsa/triumph didnt run relays for single horns .
the ..Rupert's ratio..
wiring diagrams for ... B25 /B44 ... 67
brown/blue wire ... from batt. neg. to horn
brw/blk wire ... from horn to horn-button ... button is a momentary-contact to ground battery
has a fuse to ground on positive side
a lead acid battery
drains about 5% per month all on its own .
and any drain from the horn only happens
when the horn button is pushed and the horn circuit is completed .