I replaced both headlights bulbs 6 months ago because the passenger side HID bulb was turning pinkish. Yesterday I noticed the drivers side headlight won’t turn on. I checked the fuses and there fine. Could this be a ballast or ignitor issue?

 

yes. replace ballast

 

Could be the ignitor also. The only sure fire way to find out is to replace one at a time and see which works.
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check the igniter before replacing the ballast.

 

Are the left and right side parts interchangeable?
If so, you could just swap and check.

 

they are.

 

If you have the time, patience and proper tools you can replace them on your own. On the drivers side you will encounter the cold air assembly that blocks the last two bolts to the headlight assembly. You'll need to remove bits of that before you can get to the those bolts. On the passenger side you have the wiper fluid bladder and pump partially blocking the last two bolts.

You can get an OEM Ballast and igniter off Amazon for $145.

 

Check ebaY. There's actually good aftermarket ballasts on there for around $50.
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Good and aftermarket in this application don't go well together. The OEM Matsushita ballast is rock solid. I'm usually a fan of aftermarket (Morimoto) for other cars and retrofits but for the TL, I plan to stick with OEM)

 

That of course is your choice, but I have an aftermarket ignitor installed for over a year now without any issues.
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Does anyone have recommendations on where to buy ballast and igniter?

 

https://www.amazon.com/Xenon-Ballast...dlight+ballast

https://www.amazon.com/Xenon-Ballast...CW9X2HXQZM0KF4

 

OEM Acura TL 2008 HEADLIGHT parts