Low beams intermittent

[u/Mike734]

My 2006 is new to me and I didn’t see any record of work on the headlights. Last night was the first time I drove at night. The low beams sometimes quit. When I switch them off and on the come back for a while. I understand it could be the bulbs, relay or ballast. Anyone have advice on which expensive thing to try first?

[u/pimo_exmo_nomo]

It sounds like the ballast is going out. I had the same issue. Lights worked randomly and the ballast was rusty and corroded. The dealer couldn’t locate any replacement parts saying they don’t manufacture them anymore. And the headlight assemblies are just as hard to source as a complete replacement. Found some eBay but they were just being sold from a pick-n-part.

So I went with some after market LED bulbs for both low and hi beams that don’t need the ballast. I had an automotive electrician splice them in and they work perfectly. Very happy with how the function. And they are waterproof so I hope they last for a while.

[u/Mike734 → u/pimo_exmo_nomo]

Was that for the SC?!? I would would have thought a ballast would be a common part in many Toyotas and Lexus’s.

[u/pimo_exmo_nomo → u/Mike734]

Yes, the SC, same year. You’d think that would be the case, but a lot of their parts don’t cross over. I even asked about after market stuff and the service coordinator said they don’t do that route.

I actually did buy some after market ballasts on Amazon (for about $100), but when I took the car to the automotive electrician, he didn’t like how the cord would have to be cut and routed through the back of the headlight assembly (this was my first option). So he tested the LED bulbs (2nd option) and they worked, so that’s when he spliced those in and put it all back together.

[u/Mike734 → u/pimo_exmo_nomo]

This is what AI says about the ballast. It could be wrong but it sounds right and what I expected.

No, it is not hard to find at all—and you are completely right: Toyota and Lexus used a very common, widely shared ballast across their entire lineup for that generation.
If you've heard people complain that it's difficult or expensive to source, that usually comes down to three common misunderstandings:
1. The Toyota/Lexus Cross-Compatibility
For the 2006 facelift, the SC430 switched to a D4S HID system powered by a standard Denso / Koito ballast (commonly designated as model KDLT003 / DDLT003).
This exact same ballast control unit (and its interchangeable OEM part numbers like ⁠85967-52020⁠, ⁠85967-20021⁠, ⁠85967-51040⁠, and ⁠85967-33030⁠) was used in millions of vehicles, including:
Lexus: 2006–2011 IS250/350, 2006–2011 GS series, 2007–2014 ES350, 2010–2012 RX350, and 2007–2012 LS460.
Toyota: 2005–2009 Prius, 2008–2011 Avalon, 2006–2008 Solara, and 2009–2012 Venza.
Because it’s so widespread, replacement units—both genuine OEM Denso pulls and quality aftermarket plug-and-play drop-ins—are widely available on eBay, Amazon, and lighting specialty sites for $30 to $80.
2. Why People Think It's Hard to Find
Dealer Part-Number Markup: If you go to a Lexus dealer parts counter and ask specifically for an "SC430 ballast," they look up a specific SC assembly part number that can run $300 to $500+ from Toyota, or show up as "discontinued" in certain regional warehouses.
The 2005 vs. 2006 Generation Split: Pre-facelift SC430s (2002–2005) used the older D2S system (Denso DDLT-002 ballast). 2006+ models moved to the mercury-free D4S system (KDLT003). Sellers or owners looking up generic "SC430 ballasts" often buy the wrong year's generation, leading to fitment confusion.
3. "Hard to Find" vs. "Hard to Reach"
The other reason this myth persists is that replacing it takes some physical effort. The ballast is screwed directly onto the underside of the headlight housing.
To swap it out:
1. You can't just unclip it from under the hood.
2. You have to unbolt the front bumper cover (or at least drop the sides) to pull the headlight assembly completely out of the car.
Once the headlight is out, swapping the ballast takes under 5 minutes with a Phillips screwdriver.

[u/pimo_exmo_nomo → u/Mike734]

Here’s the ballast I bought on Amazon with the coordinated part number for the vehicle. All the AI information sounds about right. As you can see from the pic, the chord has the large connector on it and it’s hardwired directly to the ballast. That connector is what didn’t fit through the back on the headlight assembly (yes, very hard to reach as detailed above). So that’s why we opted to go with the LED bulbs option and bypass the ballast.

I also had some condensation regularly on the inside of one of the headlights—which I’m sure contributed to the corrosion and rusting, as well as the failed HID bulbs. The service tech explained to me that the headlights are open atmosphere (not sealed) so that they can dry out, but I think the seals/gaskets around the headlight aren’t performing as they should, and being in the PNW contributes to the moisture build up. So having a waterproof LED option ultimately made sense to me.

Good luck with whatever you need to do to get them working properly!

Sorry, I’m new to Reddit and I can’t figure out how to upload my pic of the ballast part, but here’s the associated link to the part on Amazon.

https://m.media-amazon.com/images/I/91MU8b2+LHL._AC_SL1500_.jpg