It would be the brake bulb used for the turn signal. I don't know how the wiring would go for turn signals but when braking both bulbs are lit. If the OP really wants to go with a single 1157 bulb there are adapters on the market. <CLICK> I bought a pair & decided my 6v are brighter with the right bulbs so I took them off and modified my original bracket. OP, if you want those brackets PM me. I'll save you some money over the vendors.


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