Why does the car cut off at initial start and sometimes while driving?

Hi. I have a 1990 420 SEL that had a similar problem. I took it to a recommended foreign car repair shop. They replaced both fuel pumps and the fuel filter. This did not solve the problem, but considerably lightened my wallet. I got on the internet and found the problem-the Fuel Pump Relay Switch. This is a small black box mounted on the fire wall in plain sight. It cost me about $100 to have the part delivered and I installed it in a minute. Problem solved. It seems that