Brown plug temperature gauge sender

[Corrado1441]

My temperature gauge is not reading properly I feel so started working my way through the wiki topic on how to check if it works fine.

I put a piece of wire across the 2 terminals of the brown plug and turned on ignition but gauge did not go to full hot as expected.
I then checked C191 for corrosion but found none.
Shorted pin 4 on C101 to ground and turned on ignition and gauge went to full hot, so thankfully gauge is fine.
I then went back to plug C191 and checked wire to wire continuity, and discovered that on the engine side of the loom all pins in plug C191 are populated but on the car side pin 3 is not populated, and pin 3 being the ground wire to the brown plug, which means that putting a wire across the 2 pins on the brown plug would never make the gauge move as the earth is not connected!!

1. Should the brown temp sender only have one pin on it ?
2. Should pin 3 on connector C191 on the car side be populated ?

Thanks for any help

[Grrrmachine]

Which car are we talking about?

[Brianmoooore]

Extremely early E30s used a two pin brown temp. sensor. All except these use a single pin sensor, where the second 'pin' is the brass body of the sensor.
The wire for this second pin wasn't deleted from the injector loom, and also appears on pin 20 of the C101 engine loom socket (car body side) on some quite late E30s. This is the rogue earthed wire that causes loom meltdown after engine conversions/changes, when my 'wiring warning' in the engine swaps forum hasn't been read in advance.
The earth wire was deleted from the main engine loom, though, so pin 3 of the C101 should have a pin on one side and not the other.

[Corrado1441]

It's a 1989 325i sport.
The brown wire on loom C101 is a permanent feed so that explains the missing pin on C191.

Thanks for your answers, will try shorting pin at brown plug to chassis ground see if that works.