This is a OEM replacement ballast for several Nissan and Infiniti vehicles. If one of your headlights keeps shutting off or doesn't turn on at all, it's probably the ballast. Swap bulbs to rule out a bad bulb. Access to the bulbs is from a removed fender liner.
To install the ballast, you'll have to remove the headlight assembly. On the new ballast, take the phillips screw out that holds the wires down and disconnect the connector (use caution when doing this). After removing the old ballast and wiring harness, route the harness through the headlight and reassemble everything in reverse order.