Due to age and metal fatique, window regulator failure is very common in the W116 chassis that was built from 1973 to 1980. The driver window fails most often because it is used more than the others. If the motor is running and window is not moving it most likely is a broken regulator frame or the arm has come off the bottom of the window. If the motor does not run first check your fuses, then suspect a bad switch. You can remove the door panel and check the motor directly with 12 volt power to determine if the motor is working properly.
Problem & Solution
Common among these chassis:
You will have to remove the door panel to troubleshoot, repair, or relace the regulator assembly and it is not a "piece of cake."
Follow along with Kent's YouTube videos as he discusses the failure on the driver's window of his own W116 300SD in part 1. In Part 2 he will show you what actually failed. W116 Sedan Power Window Failure Part 2: This is What it Was!
If you need complete step-by-step instructions to remove a W116 door panel and replace a front window regulator see Kent's on demand video manual under related products.