where does this go?

[Kaasler, Ingvar]

Car: 1989 200 Turbo Quattro with MC1 engine
        
 After rebuilding and reinstalling the engine this summer, I am left
with an unconnected plug.
This is a two conductor plug that comes out of the same harness as the
radiator thermoswitch. The three wires are about 18 inches long, One is
a yellow with red stripe and the other two are brown with black stripe.
The only reference in Bentley shows it to be "Coolant temperature
sensor". Where should this plug in? I can't find any place where it
might have been plugged in.

Thanks,
Ingvar Kaasler