For the coolant temperature sender you should measure the resistance between
the two pins
I am not so sure about that, the wiring diagram does not cross streams between these, one is gauge, one is dummy light. 99% sure it is pin to base.
I have a ST, and when this gauge madness FIRST started on the drive to South Dakota for the 928 meet a few years back.. in the high desert at 110+ degrees and AC on, the ST in the car was logging 220-222 degrees between both NTC-II outputs.. but the light on the gauge was coming on well before that.
That light should not be on below 244 degrees.. that much is documented.
But I did find a cross reference to VDO for this sensor, and I have attached it's data sheet.. and my sensor is...working perfectly! (VDO 323803001020D)
Temperature range: +40 °C to +120 °C
Thread: M14 x 1.5
Sender resistance range: 287.4 - 22.7 Ohm <--Fat pin 6.3mm
Sensor signal: 1-pole common ground
Warning contact: 115 °C ± 3 °C. <--Small pin 4.8mm