Hello Folks

I've got a problem identifying a loose electrical cable dangling behind the brake's power booster. This cable has a round plug with three male prongs. I traced the wires back which concluded to three connections. Two of the connections were to sensors located between glow plugs on the cylinder head. The third was hooked to a sensor mounted on the injector pump.
After spending a few days on this riddle I cannot locate the counterpart female plug. Anyone recognize this? Or can anyone trace where these connections belong on their MB?

With Regards,
Peter - 1984 300D