How do you have a dual bulb with a single filament? By dual bulb do you mean two contacts on the bottom? If so you have the wrong bulb. If you're still 6v you need a #1154 bulb. 12v would be #1157. Those are dual contact dual filament bulbs. The reason you're getting the same light with both wires is you're feeding the same filament through either contact and the ground is being made through the housing. Put the correct bulb in it & see what happens.
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The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.
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