Ecu 5pin's on system ballast 2 slots

I'd say you have a legitimate "5 pin" there. The reason the readings are different--and of course why I suggested it, is that you are reading through various solid state components---transistors, resistors, diodes, etc, and when you reverse the meter polarity, the various transistor and diode junctions change the reading.

If it had read "infinity" or dead *** ground (close to zero) both ways, I'd have said you have a 4 pin.