My 38 has the horn relay for the accessory horns (called Town & Country in '39) connected directly to the battery (top of the starter switch), then grounded through the horn button. My regular horn does not have a relay and is connected on the (-) side of the ammeter. That was per the instructions that came with my harness.

Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.