There should be a large red wire (+ positive) at that plug that comes from the blower fuse. Also a large black wire that is ground.
The smaller yellow wire is the control voltage from the A/C pushbutton.
IF you measure voltages between the yellow & black wires then you will have from 1V to 6V, depending which blower button is selected.
IF you check the voltage between the red & black then you should have battery voltage.
All with the connecter pluged in of course.
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