W124 Cruise control box location

in my 123 in was inside the car, on the steering column. just above the brake peddle. I wouldn't worry about disconnecting the battery.

On your 124 body, it is mounted just under the cluster on the left hand side. Remove the h-lamp switch knob [it pulls straight off], remove the big nut, remove the black plastic strip starting from the left, remove the black plastic trim from the right side around the ign switch [VERY carefully starting on the left end], get a 8mm nut driver and remove all the screws that are under the black strips [the one to the right of the ign tumbler is the only one with a small washer on it], look up underneath and you will find 2 more screws....remove them. Now lower the underdash panel from the cluster. You will see the end of the cruise amp on the left.