04 model. Noticed it happening ever since I got the car back from timing belt/water pump replacement. They almost never both turn on at the same time, Ive had situations where I would keep turning the stalk for a good 10 minutes in the middle of the night before they both turn on, or I'd give up and had to rely on the fog lights.

To rule out some factors, battery and bulbs are brand new. Both bulbs are capable of turning on.. however they seldom only on at one side (drivers side). Fuse box under the hood is ok for both L/R high/low beams unless theres another fuse that relates to it.

I want to believe its just a pair of old ballast that needs to be replaced, but having both go out like this is weird. Its not expensive but I dont want to fork out $80 if the problem is else where. Not sure how else I can diagnose and narrow down where the problem is... Is there a way I can test the hid ballasts by directly supplying power to it, bypassing relays,fuses in the car, wires, etc?

 

I had TSX with intermittent HID bulb and it turned out to be bad igniter. In my case, only one side was acting like that, and once bulb turned on it would keep working for hours without problems. I swapped components side to side until I figured out it's the igniter. Power and ground were good during startup. I bought used one on ebay and swapping just that (and leaving ballast alone) fixed the issue.

You can supply power directly to the ballasts, but make sure your power supply can handle that. They produce high current spike at startup so 10A power supply won't be enough. Although once they ignite 10A is plenty. Probably easiest to simply use the car's battery.
Making sure that they have good power and ground would require oscilloscope or graphing multi meter to see what exactly happens when they turn on.

Since both sides are acting up... you have some decent bulbs right? Not the $20 ebay special.

But replacing both igniters and ballast would most likely fix the issue. Unless there is ground missing somewhere (like on the right engine mount) after the belt replacement.

 

Was just gonna say this. Sounds a whole lot like bad ground. Especially if the issue came out of nowhere like that.

 

Just replaced both ballast and igniter on both sides, problem solved! Cost around $90 and about 3 hours of my weekend. multimeter reads 24 volt or so consistantly to the wiring, so I narrowed down the problem to be anything from the ballast and after. Thanks!

 

Good that it's fixed, but get a better multimeter while you at it since there's no way there's 24V anywhere.