If you don't know the amp draw, you can estimate from the connector/terminal post size, or measure the wire diam and refer to a chart like,
en.wikipedia.org/wiki/American_wire_gauge Older wires tend to be a bit larger than new, as copper has risen they cheat on the wire. So up sizing Ga when buying new wire maybe needed.
My (49) horns have a second insulating sheath over the wires as the pass the radiator.
I'm not worried about 100 pts, but don't want a melt down after all that work for a few dollars in copper. The horn relay(batt) was fed off the generator and that was 10 ga, and the horn circuit I used 12 ga. and it fit the horn button contact connector.
There are charts for max amperage vs ga also.
Just remember 6V takes twice the amps as 12V. Amps go by diam(area), Distance corrects for wire resistance.
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