Hello Benz says this is the way to check operation so you dont replace a cluster for no reason on a 124.034 400E without a mechanical cable you should have a signal generator at left rear of trans. Checked all Fuses?
Remove the cluster and do a resistance check at cluster connector #5 multimeter between socket pins 3 (sensor) and socket 4 (grd) checking your harness and input signal -spec is 1.8k -2.2k ohms.
Also you could check ac voltage signal at same terminals should be >0.2v ac at Ten miles per hour.
Voltage at cluster same connector socket pin 2 is circuit 15 supply v and socket pin 4 gnd should have batt voltage key in pos 2
good luck Tim