After a bit of investigation and an email to TAF I think I've identified all of the parts and connections for sensors and magnetos.
The "mystery" connector is for the oil pressure sendor.
I looked in the heavy maintnenance manual and found the connections for the magnetos or Lane A and Lane B. There is a bag of parts with connector pins that are to be inserted into the ignition connector with 18 awg shielded wire.
There is also a mating connector for the tachometer connection, and my Garmin sensor kit includes a couple of diodes and a resistor for connecting it to the GEA 24 EIS module.
