ok this seems strange.. I dont have a OHM meter just my fluke Voltage tester on me right now it does continuity...

Anyway the SRT 6 air pump has 2 wires One Kind of a brown color and a larger black wire both on the same plug.. I ran my continuity tester from pin 4 on the plug. and then to the brown side of the fan plug and got nothing. i then put it in the black side and i had good continuity..