Why is this connector left unconnected?

[AudiMT]

Picture 1 is from the 3-pin coolant sensor that drives the temperature gauge in the car.

The brown wire is ground. The blue/brown wire controls the temperature gauge in the dash and that's working fine. The blue-white wire, along with the blue-yellow wire from the coolant expansion tank's level-sensor, should cause the coolant warning light on the dash to flash if the coolant temperature is too high and/or the coolant level is too low, respectively.



I traced the blue-white wire to the 5-pin red connector shown in picture 2. There is nothing for this to plug into. You can also see a couple of blue-yellow wires in there, connected to one pin. These blue-yellow wires connect to the correct pin on the instrument panel that causes the coolant warning light to flash.

From all the wiring diagrams that I've seen (I don't have the wiring diagrams for my exact model of car), the blue-white and the blue-yellow eventually get tied together somewhere in the chain so either, or both, can trigger the coolant warning light on the dash.



This discovery came about because I've been trying to fix the instrument cluster on my Audi 80. In order to test the warning lights, I've been triggering them by connecting the relevant wires to ground which then simulates the fault. The cooling warning light should have come on when the blue-white wire was shorted to ground at the sensor's wiring plug but it did nothing and so started the investigation...

The way things stand at the moment, the coolant warning light will only flash if the coolant level is too low. It seems to be that way by design but it seems a bit strange to leave one out. If I jump the blue-yellow and the blue-white wires together in the connector (easily done), I should get both warning functions.

Any thoughts on this?
 

Edited September 3 by AudiMT