Radiator Fan stuck on (A100)

[ovalking]

Connected up the battery after winter hibernation, and the radiator fan started running - made me jump! It won't stop, so have unplugged the motor connector for the moment.

1988 Audi 100 with KU engine.

I checked the resistance across the terminals of the thermo switch screwed into the radiator - that is correctly open circuit.
However, I measured about 1K* across the terminals of the disconnected thermo switch plug (so not a clean short, but I was expecting open circuit). I measured 60* between one pin and ground (probably as expected). What is correct?
I removed relay no. 2 and confirmed it is open circuit between pins 30 & 87, so the relay is not stuck.

Ideas on what to check next appreciated.