As I thought, there's something off with the fuel selector.
from the BAL-manual Feb 1940
BAL Teil 7.jpg
This should be for C-1 and C-2 series. (tank pumps)
From the "Betriebsanleitung und Rüstanleitung" June 1939. (single pump)
Bf 110 C-1 C-2 .jpg
From "BAL Teil 12" but only for D-Series I think.
Bf 110 D-0.jpg
And from the Kurz-Betriebsanleitung (KBA from Feb 40) an additional attachment from October 1942.
C-series october 42.jpg
The interresting is that in the KBA already 2 pumpsystems are mentioned.
An old one with a central pump and a new one with seperate pumps for the tanks.
The "Ersatzteilliste Teil 7" from Jan 1940 doesn't even list a single pump, only the valve switch and the tank pumps.
The only conclusion that I can see for this is, that the B-series and first and early C-1 C-2 had a single-pump. In production of early C-series the pumps-system was changed to seperate tank pumps with the valve switch.
And if you compare the valve switch system from the C-Series (C-1 C-2) with the D-Series, they also work differently. The E-series uses the same valve switch system as the D-series.
Mankau/Petrick mention in their book a change in the fuel pump system and problems with the quantity of them for the production of the D-series as a sidenote, but didn't go into detail. Maybe because of the "Dackelbauch" with 3 additional pumps, but that's only a speculation of me.
Did anyone has more info regarding this matter?
Edit: after looking more closely to the diagrams I realised that the 2. Pic shows the single pump system.
But there is still a difference between the switch position of C-series tank pumps and D-series in the drawings.