My father did almost the same thing as you did. He had an earlier Sebring Convertible & just traded it in & got the SL550 Convertible. He got a great offer for his Sebring, since there were hardly any miles on it, & then he took it one step further & used the KBB Search feature to find the best price on a low mileage SL550 & found one about 100 miles away in Chicago. It was worth the drive too, as the local MB Dealer didn't want to come down hardly at all on his price, but the Naperville MB Dealer came down several thousand dollars.
The only downside is he wanted the same Bright "Purplish" Blue HID's factory equipped, but knew that I'd done this same upgrade on my C230 Sport, so for about $100 I ordered a kit from a distributor I use who carries the good quality, digital HID's that won't throw codes or mess with the computer built into every Mercedes.
I had to go through a few "lemon HID kits" before I finally figured out that you don't need to spend hundreds or more on a top-of-the-line kit, when you can get a kit that not only fits beautifully, but works even better than any other kit I've seen or heard about when it comes to upgrading to HID's on a Mercedes. For $110 + Shipping I can get a Digital, Slim Ballast HID Upgrade Kit that any backyard mechanic can install in under an hour. It plugs right into the factory plus, so it doesn't get any easier than that. I've done this conversion probably a dozen times or more & in all that time I've NEVER had a single one returned, never had a problem with it throwing codes or throwing out voltage spikes either.
In fact if you EVER need a good HID Kit I can have one sent to you direct from the manufacturer I use, & like I said they're very simple to install. You can find videos all over YouTube if you do want some help, but I doubt highly you'll need it. It's not much different than changing a standard Headlamp, except that you're adding a ballast unit to change the voltage & regulate it.
Whether you decide to do the upgrade or not, or whether to buy it from me or not, this advice is free: DO NOT, I REPEAT DO NOT make the mistake of buying a cheap HID Kit that doesn't have a digital ballast system. If you don't get the digital ballast you will likely have problems with the unit at some point, so it's worth paying a little more for a better quality digital HID Upgrade kit.
Feel free to text me or email me if you have any questions or problems...
TEXT: (260) 445-5241
I own a small IT/Tech Support/Electronics firm, that does everything from fixing computers to installing whole networks & even some background & investigative work in between. That comes from 4yrs of college & 20+yrs of experience, so I really do know what I'm talking about. I don't mind helping if you have a kit you've already bought & are stuck in the midst of the install process, so text or email me anytime, whether to buy a kit or just for some free help/advice!