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With a flashing light, this won't work well with a digital meter because they respond too slowly. However, since the parking light filament uses the same ground, just turn them on, connect the meter in DC volts mode and go from the negative battery post to the brown wire in the lamp connector and the meter will read the voltage drop in the wiring to the ground stud which should be very low because of the short run. You could do this on the left side as a comparison so you know what drop to expect. The ground stud is most likely on the fender well nearby. Maybe.

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Roger E.