I assume you just don't understand. The fuel pump relay takes power from the connection above. When the relay is in the group of appliances (warm-up reg, freq valve, lambda controller and FUEL PUMP) are turned on.
Since the fuel pump seems to work the circuit obviously does its job. Since none of the appliances are absolutely necessary for running except the fuel pump, it is resonable to figure that none of them are the problem UNLESS their excess cuurent or just normal current causes the connection at C105 to break down. In this case the circuit to the ignition is taken down.
This is my hypothesis, IT MUST be understood to be proven. It is absolutely easy to prove, but you have to understand what I'm saying. If I'm right with this hypothesis no amount of parts will fix it. I am saying that one of those phillips screws is loose. The lead that goes to the ignition must maintain battery voltage to power the ignition. Check it out.
My hypothesis supposes that the pump runs doesn't ever run with the fuel pump relay out, not even while cranking or first turning the key.
Bosch Master, ASE Master, L1
33 years MB technician