Sequential turn signals
Sequential turn signals are a feature on some past-model cars whereby multiple lights that produce the rear turn signal do not all flash on and off in phase. Rather, the horizontally-arrayed lamps are illuminated sequentially: the innermost lamp lights and remains illuminated, the next outermost lamp lights and remains illuminated, followed by the next outermost lamp and so on until the outermost lamp lights briefly, at which point all lamps extinguish together and, after a short pause, the cycle begins again. The visual effect is one of outward motion in the direction of the intended turn or lane change. This implementation has generally been found only on American cars that use combination red rear brake and turn signal lamps.
Sequential turn signals were factory fitted to Ford Thunderbirds built between 1965 and 1971, inclusive, to Mercury Cougars between 1967 and 1973, to Shelby Mustangs between 1968 and 1970, to 1969 Imperials (built by Chrysler), and to the JDM 1971 Nissan Cedric. The system is costly and complex relative to standard turn signals, and no other production cars were so equipped.
Two different systems were employed. The earlier, fitted to the 1965 through 1968 Ford-built cars, was electro-mechanical, featuring an electric motor driving, through reduction gearing, a set of three slow-turning cams. These cams would actuate switches to turn on the lights in sequence so long as the turn signal switch was set. This system was complicated and prone to failure, and the units no longer function in many surviving cars. Later Ford cars and the 1969 Chrysler Imperial used a transistorized control module with no moving parts.
FMVSS 108 has been officially interpreted as requiring all turn signal lights to illuminate simultaneously. However, the 2010 Ford Mustang is equipped with sequential turn signals.