Sprop,
It would help to know what year your car is, also what model. For instance, I have a 126 and it has 5 speeds. Low and high speeds are manual (push buttons) and 2,3,and 4 are automatic. A friend of mine has a 126 and his goes from low to high in auto with a botton for low or high speeds only. So 124 is not enough information to receive a correct answer.
By the way, my 126 is an 84 500SEL and my friends is an 87 420SEL. When talking about the electrical system the year and engine is just as important as the body style.

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84 500 SEL (307,xxx miles)