The red rocker switch for the 4-way flashers serves two purposes. First, it allows you to turn all 4 flashers on, by rocking the switch into the "on" position, which then energizes the blinkers at the four corners of the car by sending a signal to the blinker relay for all four blinkers at the same time (something the blinker stalk can't do). The rocker switch is not the item that handles the current to the blinkers at the corners, and it is not the thing that has the relay in it that makes the noise or makes the lights actually blink. Next, it prevents you from using the turn signals when the 4 way flashers are on. This means the signal from the blinker stalk goes through this little switch, and if the switch is in the "emergency blinker" position, the circuit to the blinker relay from the turn signal stalk is interrupted. So, if the little red switch fails, it can disable the blinkers. The blinker relay is another part, and runs the bulbs in the four corners of the car, as well as the instrument panel arrows, and the little lamp that lights the red rocker switch when it gets a signal from the blinker stalk or the red rocker switch.

I hope this helps. Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)