It has come to my attention that the 2010 Mustang apparently has sequential rear turn signals; however, my understanding has always been that they were prohibited by FMVSS 108 and in fact a quick google turned up a reference to a "docket 15333" 6/3/03
Sequentially illuminated LED stop and turn signal lamps are not permitted. All light sources must illuminate simultaneously. During the initial stage the stop and turn signal lamp would not comply, in this case, with the minimum luminous lens area requirement. Additionally NHTSA does not consider lamps with a changing illuminated area to be steady-burning.
could not find full text of said docket, only a reference to it.
But... go to Ford's web site and sure enough they are advertising this as a design feature of the new 'stang. Now I think they are cool, they're certainly far less of a hazard than some things that NHTSA has permitted (high beam DRLs, HIDs without levelers, lack of requirement for turn signal repeaters, etc.) but what gives? Can't find any reference to a rule change or reinterpretation...
nate