have a 2003 F-150 4x4, went to use the four wheel drive the other day and it doesn`t seem to work the rear tires just spin, lights on the dash come on and it sounds like it is engaging when you turn the switch but nothing. Any ideas?

 

From what you say it sounds like the front actuator in not engaging.
This functions last is after the the system operates so can't be detected becaue it's a mechanical funtion wth no sensors.
Check the vacuum lines from the solenoid relays on the firewall to the actuator located on the left front axle housing and it's ability to operate a collar inside to lock up the front wheels.
Good luck.

 

spray a little penetrating oil wd40 on the front actuator and run it back and forth a few times will usually free it up and be fine for a while I do mine a couple times a year.

 

I found some vaccuum lines that are plastic that run from the front rear end up the frame and under the battery box and connect to these units on the firewall, two of them were broken from the acid dust off the battery and thats why my four wheel drive isn`t working. I could fix the lines with some rubber hose, but I have one line that I can`t find where it goes.I have a pink and light blue that connect onto units on the firewall but I have a black one that looks like it came off somewhere and not broken but can`t figure out where it goes, took the battery out but can`t see anything.

 

I found two broken vaccuum lines under the battery box, a light blue, a pink and a black one, I can see where the pink and light blue one connect to on the firewall but can`t find where the black one goes to.I can fix the two broken ones with some rubber hose, don`t know what to do about the black one, or if it even goes anywhere?

 

the black one may come from the intake manifold and connect to the vacuum canister behind the battery, inside the fenderwell.

 

What he says, you haven't noticed your vents acting goofy wether pedal/no pedal? If the resevoir isn't working this is usually what you notice first. Air defaults to the defrost. Ask me how I know this