The motor probably just has a temperature switch that goes open circuit when it gets hot enough.

I wonder if the drive is looking for a thermistor, in which case try leaving the wires disconnected.

NTC thermistors are more common (resistance decreases as temperature increases), so I'd guess if that's what the drive is looking for, leaving it open circuit is less likely to trigger a fault. Failing that, try a 2-3k resistor.