Relays dont care about polarity or voltage,what a relay does is allow you to control a high amperage circuit with a milliamp control,basically you don't run the horns load through the button.Modern electrical systems use relays to reduce switch loads and provide full load to the component .Its no where near period correct,but its a better way to skin the cat.I used relays and modern fuses to protect all my circuits..It makes troubleshooting easier and my harness wont burn if something goes wrong..
