@Yveaux
Yes, it's a pt1000 sensor.
Is it possible to use the existing sensor on my solarcontroller and in parallel with an arduino or do I need an additional sensor?

I want to measure the temperature of my pool. I already have a Sensor in my Pool Equipment from the Solar Controller and I want to use this.
Unfortunately this Sensor has only two wires and it's only a Resistor I guess.
Is it possible to use this Sensor for Temperature monitoring?

Thanks.
It was a wrong cabling.

I programmed many times a NodeMCU with some sketches and Wifi was always working.
Due I am totaly new to MySensors I copied the example sketch for ESP8266 (https://www.mysensors.org/build/esp8266_gateway) edited my credentials and uploaded it. But Wifi is not connecting to my Router.

⸮HQȸ⸮⸮ld⸮xO⸮⸮76 MCO:BGN:INIT GW,CP=RNNGE---,FQ=80,REL=255,VER=2.3.2
134 TSF:LRT:OK
150 TSM:INIT
163 TSF:WUR:MS=0
186 !TSM:INIT:TSP FAIL
210 TSM:FAIL:CNT=1
230 TSM:FAIL:DIS
248 TSF:TDI:TSL

What is missing?