1999 ML430; 1998 S420
For some reason, my iPhone charger would not stay securely in my ML's cigarette lighter socket. It was constantly coming loose. So I bought a quick charge USB charger socket off of Amazon for around $13. (it says the brand is ADSDIA, but it looks exactly like other unbranded ones that are cheaper on eBay). It was very easy to install, and works perfectly. Problem solved.