Have a '06 f250 with EOFS and auto/manual backup hubs. Turn the switch to 4wd and you get Defrost for about 45 seconds. I realize this could actually be normal because it goes back to the regular mode. The transfer case goes into 4wd, but no light on the dash. Does not lock the front hubs. I can put them to manual lock and the 4wd system is working. Put it in 4wd low and it will go into 4wd low, but no light. I traced the lack of auto hub function to the vacuum solenoid. It is either not working, or is not being commanded to work. Either way it's not sending vacuum to the hubs. Without the hubs using the vacuum system, what else does the 4wd use the vacuum for? Seems like 45 seconds worth of vacuum is excessive without the hubs using any vacuum. Also, what actuates the dash lights? What actually makes the connection for the light to come on. Is it the 4wd switch, in which case it would be a switch position indicator. Is it an actuator on the transfer case?
Thanks in advance.