So I've been working on a issue with my 4x4 (2006 F150 FX4 5.4) , no lights come on, no noise, nothing when I try to engage. So I started reading the forum, changed the actuator, nothing, just changed the solenoid, nothing. Then I started looking for the vacuum reserve box and this is what I find, NOTHING THERE AND A FREE VACUUM LINE. Is this the reason why my 4x4 isn't working and if so why, I haven't been really to find a answer. Thanks y'all!

 

Here's what I found

 

And another one, the vacuum line hanging out not attached

 

That's definitely a problem, but I doubt it's the only one. With an open vacuum line, the hubs will probably be engaged full time. That wouldn't explain why the transfer case doesn't shift into 4hi or 4lo. I would check the shift motor on the transfer case. Also check the wiring to see if the motor is even getting a signal to engage.

 

shift motor is brand new

 

Try plugging the vac line for now. See if it will engage. Also check the wiring. Make sure the shift motor is getting a signal to shift into 4wd. There's a relay under the hood for the 4wd system. You can try swapping it with a headlight relay to see if it's still good. Have you checked fuses?
It's weird that someone would take the vac resevoir out. Perhaps it was accidentally left out after a repair, or someone intentionally took it out while troubleshooting the 4wd.

 

thank you for the help, now where exactly are the relays, I've been trying to locate them

 

There's an auxiliary box under the hood. In my 04 fx4, it's on the driver side. The owners manual will tell you though. If you don't have one, you can find them online, but I forget where. You should be able to Google it and find one. Or do a search in the forum.

 

How big is it? I have a huge Volant Cold Air Intake where I'm assuming the box should be, but I saw something quick when I looked, it looked like a smaller black box. Had wires coming out of it.

 

The relay box is closer to the firewall, by the brake booster.