[cmonref]

That resistor is in series with the light in the flasher switch that glows when the lights are on, so you can find the switch easily. I'll bet that resistor is to perform the dimming, down from what might be a full bright light. Note that when the lights are on, if the flasher switch is ON, the circuit thru the resistor is opened and the switch applies full voltage to the light -- and it flashes BRIGHT with the flashers on the corners.

If it were defective ... If it becomes an open circuit (or is disconnected), the light in the switch will not burn when the lights are on. If it becomes a short circuit, the light will be steady bright when the lights are on.