rattlsnak

Problem: when I turn the blower fan switch to ON, in any speed, or at any temp setting - with the A/C button OFF, my A/C condensor fan turns on and off rapidly. 2 secs on, 2 secs off, at high speed. I read somewhere about the ballast being bad, but I have changed it, swaped out the relays and checked all the fuses, etc and all are good.
Ideas??

and believe it or not, both speeds on the rear blower fan work perfect!