The last few days, my 97 Mercedes S500 just stops while I'm at a stop light. The dashboard lights come on, and I have to restart the engine. How do I fix this?

Perform the tests below:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-11.html#post2123675

Ensure that the platinum spark plugs have been changed in the last 40,000 miles. After that, I would focus on the Camshaft Position Sensor and the Crankshaft Position Sensor. I would replace them, if they have been in for 120,000 miles. It can make a substantial improvement in performance, even if no codes are thrown indicating there's a problem with them. The intense heat of the engine is their enemy and adversely affects their resistance, over time.