Alright so recently purchased a 04 F150 FX4 from Facebook market place. Long story short it was stuck in 4wd, did a overall look and transfer case motor was bad, vacuum lines were cut up, IWE’s were rotted. Replaced the entire system solenoid, lines, you name it. And guess what? Back in 2WD. Problem is, now it won’t go into 4WD. I bought the solenoid that was supposed to be for my truck and it wouldn’t work at all. Used the original that came with the truck and it works and holds vacuum but won’t cut off vacuum to the IWE’s to put in 4WD. The part number for the solenoid on the truck is different then the one that i find online that says it’s for my year. I purchased another solenoid of the same part # that came with the truck, plugged it in, and doesn’t work at all. Not sure if the one I bought is bad or what. I know the shift motor is working good I triple checked it and tested vacuum to IWE all that is good. When I flip the switch to engage 4Lo the light comes on, but is still in 2wd (spun cv axel) . When I flip to 4hi it flashes real fast then goes away and is still in 2WD. I’m stumped. Any ideas why it flashes on 4hi and won’t cut off vacuum? Tried 3 solenoids now. Thanks guys for reading I’m brand new here, 27 years old and first time truck owner.

 

You should probbly get the 4x4 module scanned for fault codes. Im guessing if its flashing it has a trouble code logged, I had a similar issue with my solenoid, it would not close vacuum but it was gettting power from the 4x4 module. Its simple enough to check with a multimeter, check for power accross the terminals of the plug with the swtich in 4x4 or 2wd, i can't remember if it energizes or denergizes to shut off vacuum but if theres no power in both 4x4 or 2wd you have a wiring/power issue.

 

Do you have the 10th generation "Heritage" or the 11th gen new body style 2004?