When I bought the car the guy had in some Dynamic Diode lights yellow ones. One failed. Swapped them out for some on Amazon. They lasted 7 months and one failed. Replaced them with more off of Amazon.

Now 1 of them is out again.

Any idea what would cause it?

Any recommendations on new replacement bulbs?

same side? try using Philips OEM..
aftermarket ones don't last too long.. my Morimoto's are flickering after a year.

I wish I could remember which one failed before.

i've "heard" most aftermarket bulbs only last 1-2 years... so try a higher quality bulb..

I get 2 years out of my DDM tuning bulbs before they color shift and fail.

Honestly...cheap, aftermarket Chinese bulbs...should pretty much explain it all.

There's a reason why the Phillips OEM ones are pricey.

I finally remembered where I ordered them from.

Luckily I made an account with them, and called them today. They shipped out a replacement today, with no hassle at all.

Shout out to Diode Dynamics for great customer service.

I just wish the bulbs were not such a PITA to change.

I had a headlight bulb burn out in January, right in the middle of nonstop snow and 5 degree temps. I didn't have garage access at the time (couldn't roll the Mustang out) so it was no fun laying in the snow in the pitch black after work trying to change out those bulbs.

205k, 10 years and still on stock hid bulbs.

Phillips bulbs are hard to beat. My 2004 just had its first headlight failure and I bought Phillips replacements off of Amazon.

You are aware HID bulbs color-shift as they age?

They do still work though.. Point made.

Mine still look white/blue. I am sure they will explode like my hub did, lol.

I'm sorry. As much as the situation sucks, that made me

The problem is the quality of bulb. most bulbs i have bought off of ebay or amazon either have issues lighting and staying lit or crap out within a year. i've had really good luck with bulbs from this seller on ebay:

http://www.ebay.com/usr/ionicparts?_...72.m2749.l2754

They have been on my car for 2 years no, not a single issue.

So it seems the ballast is bad.

Any suggestions on where to get a replacement one of those?

Dealer is only one with it in stock and want almost $600 for it.