There's a 5/8" diameter horn wire hole in each 35 front fender. Would it have
come from the factory with a protective rubber grommet in these holes that
the harness went through?
Where did the OP mention a pickup?Yup....Brian's got it correct.
The horn bracket which the horn body attaches to is the bolt that attaches the headlight mount to the fender.
You should only have a single horn on you 1935 pickup.