<<The haynes manual also states that the ECU output pin on my 16 pin socket is pin3, but THERE IS NO PIN3 on my DIAGNOSTIC socket? Hence the question.
There is no pin 3 on yours as pin 3 is for USA emmissions
only with a Check Engine warning lamp system,,
However, as Jim F points out, pin #8 is Both HFM and SFI
module, And the E320, 124 chassis being the same system
and diagnostic plug, is prob close to/or same...
Why not give 8 a try and we can compare what you have for codes ....