I think the LLS compressor on my 2000 Expedition has failed, but I want to test it to make sure. There are 4 wires on the connector, one pair (red, black) is large, the other pair (black, blue) is smaller.

I assume the red/black wires carry power (12VDC) for the compressor motor itself. But what is the purpose of the other two smaller wires? How can I test the unit?

Thanks.