Which Coolant Temp sensor? 124.128 with 124.133 engine

[filp]

Hi,

Temperatures have gone up and I realized that my aux fans are dead.
Apart from that, I've noticed another issue: there's no voltage to the fans when AC is on. The voltage appears when I jump the pigtails going to pressure switch on drier. That leads me to thinking that it's either bad K9 relay or...the coolant temperature sensor is a switch and not a thermistor. The car is 1992 300D with 1987 300D engine (om603 turbo). I'm not entirely sure if the thermostat neck was replaced. The "sensor" is three prong, gray.

If it's the 87 switch, this will affect CCU readout of temperature and makes sense that the fans don't get voltage at idle.
If it's a proper sensor, it may be bad. Which replacement is ok? 006-545-42-24? Aren't the 3-prongs all switches?

When I jump the cables to 2-prongs on that "sensor", the AC cuts off. Which is correct AFAIK. In heavy traffic my AC was cut off when temperature climbed to 100...so something works.

Please help me clarify this. Yes, I used the search function.

Thanks