mystery connector in engine bay

Hi, my first time here, so here goes. Currently swapping engines (1.4 Hdi 16v 8HY) and I have one connector "left over" with no socket to plug into. it has 3 pins, it is black with yellow internals/dust seal and the wires are red brown and yellow, the code on the yellow wire is 2603 328E. as for its location, it is above the gearbox and underneath the thermostat housing and battery box. I have trawled the entire haynes manual for a three pin connector with those coloured wires but it is not mentioned anywhere. Maybe it is redundant and for a component not fitted to mine, maybe its diagnostic, or maybe I just missed the obvious. I checked the engine gearbox thoroughly and assumed it must plug into the vehicle at some point during reassembly but nothing has turned up within reach and I don't want to get any further in without a definite yes/no as I might have it all to take apart again. Please help, as Citroen (porthmadog) are next to useless over the phone (bring it in and we'll have a look!)

Is it possible to post a picture?

1st impression from your description is that it could be the water sensor wire to the fuel filter... most aftermarket filters have the sensor connector blanked off, the shape of the connector is still there to fasten a redundant wire to.

HZ