As per Ghostvette, your "auto electrician" doesn't understand how electricity works. LEDs, since they have a higher resistance than OEM incandescents, allow less current to flow (which triggers fast-blink mode). The resistor in parallel with the LED lowers the circuit resistance, raising the current to something closer to what it is supposed to be.
And the resistor will get HOT. Some people add a heat sink; some people bolt the resistor to the frame or a metal body part for a heat sink. Keep away from any plastic parts.
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