Chage the flasher swich on steering colum
Replace your temperature sensor. There is a sensor specifically for the cooling fans that triggers the relays, and tells the fans to turn on/off. The relays won't energize unless it gets a signal from that sensor.
That sounds like a bad earth/ground fault, the earth connection is enough to make your multimeter or what ever your using register but not good enough to make the headlights work.
Try and locate the common earth point for both headlights and clean then reattach it.
try running power from relay to the inertia switch through a jumper wire and see if pump works. you might have a pinched or broken wire in the factory harness.
one of those three prongs sould be ground, one should only come on with the high beams, and the other only with the head lights. if all three have 12v power you have a short somewhere.