If I remember correctly, the outermost terminals are the LEDs on the defrost switches, but it's really best to pop the switch apart and test them directly.
The notched side of the LED is negative.
Diode check is usually marked on the meter with a diode symbol, like this:
The diode check will illuminate the diode, though dimly. Again, best to remove the switch top to best ter see/test. It pops right off with little rocker tabs on each side.