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How to fix a burned out signal bulb
Purchase the right bulb for your vehicle.
There are many variations in the bulbs used by auto manufacturers, so it's important that you get the right one for your vehicle. You can find information pertaining to what bulb to purchase in your vehicle's owner's manual.
If you do not have the owner's manual, you can ask the clerk at your local auto parts store to assist you. You can also find bulb information on the automakers web site.