I have a 2004 g35 coupe. I bought new headlights and headlight ballast. When I first turn my key both lights will turn on but if I keep my vehicle running and shut my lights off and turn them back on the driver side low beam doesn’t turn on. Any one know the problem ?

 

Swap components one at a time from the driver to passenger side until you isolate which component is the problem.

I would start with the ballasts.

 

I put brand new ballasts on each side that’s not the issue. It’s only my low beams everything else works fine. Idk what else it could be besides wiring

 

That doesn't matter
Follow Cleric's advice
Just because a part is new doesn't mean it is good. Haven't you ever heard of out of box failures? Quite common.

 

Did this problem exist BEFORE the new lamp/ballast? From your post it sounds like you put in the new lamp/ballast then the lights started malfunctioning. Clarify.

The reason for swapping the components, you might have purchased a DEFECTIVE "brand new item", the logical troubleshooting steps are to start swapping components that are known to work (i.e. the other side of the car) with the side that is currently malfunctioning.

Once you have swapped the ballast, driven and verified the problem still persists, then swapped the lamps, driven and verified the problem still persists, THEN you have eliminated those two components and being faulty. At that point you can start diving into the harness.

There is also a ground wire for each headlight that you should unbolt, wire brush the lug, bolt, and the chassis surface, apply a small amount of electrical anti-oxidation grease (not dielectric for spark plugs...), then bolt it back together. The grounds are located in the engine bay on the front of the wheel wells, small gauge wire on a ring terminal bolted to the wheel well.

 

I thought the same thing with the new ballast being defective so I ordered another new one and it did the same thing. I’ll have to try re grounding it and get back to you on that thank you