E36 temperature gauge woes

[Loom]

Please help me out on this one; car in question is an E36 316i. The temperature gauge does not work most of the time. It stays on the far left on the cold side and only sometimes it would start rising to between 1/4 and 1/2 way through and then drops to the resting cold position again.

I've removed the intake manifold to replace the engine coolant temperature sensor only to discover that the sensor is working fine. It's the dual sensor with pins 1 (brown/yellow) and 2 (brown/purple) for the temperature gauge and 3 (brown/red) and 4 (brown/black) for the ECM.

I've done the following:

• Instrument self test - needle works fine
• Swopped another car's instrument cluster - both works in the other car and not in the 316i
• Tested voltage on pins 1 and 2 - it's about 3.5 or 3.8 V
• Tested continuity of wires
• Put in various low value resistors in the sensor connector - the needle rose once or twice as it should but could not repeat it thereafter
• Same as above but with a resistor connected directly to the wiring connector at the instrument cluster
• Eventually cut the 2 wires at the instrument cluster to rule out any leaks/shorts and did the resistor test directly at the cluster, again with no success

So the instrument cluster as well as the sensor apparently works fine, pointing to faulty wiring but the last test ruled out the wiring and it still does not work.

I'm at wit's end. The only other thing I can think of is that the wiring is wrong at the instrument cluster so I'm actually working on the wrong pins.

What else can I do?

 

[Loom]

Update:
turns out that the sensor was faulty but knock knackered enough to give a faulty resistance reading. After replacing the sensor everything seems fine.

I took some pictures and will try to do a write-up on removing the intake manifold of an E36 316i.