I think you just measure it between the yellow and the black wire. they both go to the ECU to deliver the voltage reference.

FFT, if that black wire is spliced & then goes to map its
a sensor ground,you would test it on the yellow wire.
As the sensor starts to complete the ground the ref
wire voltage will drop. The ecu sees the difference
and uses this to sense engine temp. DonMan,you
said the engine runs extremly rich at idle but gets better
when rpm up. This could be the map, if there is no vacuum at
map or the return ground is open to the ecu,the ecu will
see a full 5 volts on the map signal & the temp signal
this will cause it to run extremly rich. With fuel pressure
o/k something is commanding injectors pulse width higher
to add more fuel, tps could do it, map or coolant but not Iac.
I think you have to test map & coolant sensor first