I’m installing a new horn in my 1953 GMC and need some help. I tested the horn hooking it to the battery and it works. I checked the wire continuity from the horn to the horn relay and it’s ok. I don’t have a horn button but when I press the horn ring nothing happens. Is there a way to test the horn relay? Does the horn work without the car running or does the key need to be turned on? I’d appreciate any ideas on what to check next.