1988 300SE W126 CRAZY FUEL PROBLEM......

[BigRed0803]

This car is about to drive me crazy, I have checked all fuses including OVP, this is what the car does, it will start up fine run great and after around 20 seconds it will die, you can start it right back up and it will do the exact same deal time and time again. Well first I figured fuel pump relay, I jumped it at the relay so it would run all the time. The problem was the same car would run great for around 20 seconds then die. I know how common fuel pump relay issues are on this model so I ordered a new relay but the problem was still there. I got under the car while I had a buddy help me sit in it and crank it and found that when the car is running I have juice at the fuel pumps with my test light, as soon as the 20 or so seconds are up the juice leaves the fuel pumps and that is when the car dies. I probably tested it 5 or 6 times and each time when he would start it my test light would be lite up and then all of a sudden my light goes out and the car dies. What could be causing this, it is obviously not my fuel pumps sense they aren't getting any current and when I do have current it runs perfect. It also can't be my fuel pump relay since I replaced it with a new one straight from the Mercedes dealer. I thought it could be something wrong with the electrical ignition piece at the ignition switch so I replaced that also but still have the same problem. What other parts could all of a sudden kill the power to the fuel pumps? All help is appreciated. Thanks