[blucar]

Not a good idea to connect accessories through the EFV8 ignition switch's, they were never intended to carry more load than just the ignition.
Many of the '35-37 Philco Ford radios I have seen, the one in my '36 coupe included, have a toggle switch for off/on incorporated into the radio box, the control head also has the off/on switch. I would surmise that the toggle switch in the box was a safety feature to prevent leaving the radio on and draining the battery.