I have a 94 C220 with 52K miles. I never encountered shutdown during driving. But a couple of months ago, it just could not start. Following this web site for a period of time, I had idea in mind that it most likely be the OVP problem. I used a multimeter to measure the pins according to the diagram on the side of OVP. I found one pin from the smallest relay, Sorry I don't remember it's pin9 or pin12, has no 12V voltage coming out. That's the problem. Replace with a new one, everything is fine till now. You can try to diag by yourself.