My 06 DTS headlight problem started with the lights flickering, and then returning. When the car was out of warranty, I was informed I need a $900.00 light. I found one at the wrecking yard for $600.00. After the intense installation, it also blinks. Now both lights blink, and go off. You have to switch them off, and then back on, to acheive lighting. Most of the time, we at least have one light. I think that GM should recall this, as a manufacturing defect. They should at least offer a fix.
Our dts does the same thing. One headlight would blink - dealer said they could do nothing unless the light was not working, Finally, it was out and I took it to the dealer. The replaced the ballast at a cost of $590. Said they have to take the front bumper off to do it. Now trhe other one is doing the same thing. Just a poor design. GM is ruining their already bad reputation.
My 2006 DTS does the same thing. When I first got it the left headlamp would go on and off. Took it back and they replaced it for free. Two years later, the right headlamp will go off, flicker, if turned off and back on it will be on. I have a friend that also had a DTS and has the same issues. I wish Cadillac was like it was 50-60 years ago and was a car you could be proud to own. Now with all the electrical/computers things mess up all the time. This definitely should be a recall being everyone I know with a DTS has the same issues.
I've had the exact same problem with my 2002 Nissan Altima. It turned out that I needed a new alternator. The job cost me around $400 (parts and labor), but the price depends on the car model you have.