My AC and heat seem to work if I'm going down the highway and air is forced into the ducts due to highway speed. But the blower motor will not come on. I've removed the cover under the hood and when I connect it directly to the battery it spins fine. I've actually verified with an ohmmeter that the fuses are working OK. And since the two relays are the same in the fuse box, I swapped them. The blower still doesn't work but everything else in the car does. I also looked for obvious vacuum leaks under the hood and everything seems OK. The diaphragm modules I could reach hold their vacuum when I draw it. I then removed the center panel in the car and checked for voltage at the fan speed switch. I have no voltage whatsoever between any pair of pins. Where does this switch receive it's signal from? The wire bundle doesn't conect to the a/c panel but goes somewhere under the dash. What could cause the blower to not be coming on?

Thanks.