if you look at the wiring schematic for the Packard there are numerous splices, connectors, circuit breaker, the Light Switch, flasher circuit, bulb base, etc. Add 60+ years of corrosion both to the actual wires, and the all the connection points and switch internals and also figure if you are running at night you also have more load through the switch due to the headlights, dashlights, etc. Now add the quality of the bulb socket ground to the mix.