Sorry, I hit submit to fast before finishing post! Traditionally red will be positive and black negative. If you know how to use a DC voltmeter you can determine which one should be red and black. If you don't know how to use a meter, take the charger to your local Autozone and have them test it. You can always buy red electrical phase marking tape at lowes and I would use tape to mark the red. The previous post is in case you need to replace the ends. Sorry, I hit submit to fast before finishing post! Traditionally red will be positive and black negative. If you know how to use a DC voltmeter you can determine which one should be red and black. If you don't know how to use a meter, take the charger to your local Autozone and have them test it. You can always buy red electrical phase marking tape at lowes and I would use tape to mark the red. The previous post is in case you need to replace the ends.