A friend of mine has an '01 F-150 4x4, and 4WD will not engage. I tested the vacuum acuator on the axle, vacuum lines to it, vacuum solenoids on the firewall, etc. The T-case is manual, and is engaging properly. If I manually apply vacuum to the appropriate hose, the front axle will engage, and disengage. When shifting into 4-hi or 4-lo, the lights on the dash do not come on, but both bulbs are working, as they come on briefly when the truck is started. I wasn't able to check the switch on the T-case itself, but I tested the wiring to it, and there are 5V going to the switch. I tried jumping the 2 pins on the connector, but still no difference. Both vacuum solenoids on the firewall are getting +14v across the connectors. It would seem like there's a relay that should be actuated by the T-case switch, and switch the 4WD light and vacuum solenoids, but I didn't find it in the owner's manual, and don't have access to the shop manual.

If anyone can shed any light on this situation, I would greatly apreiacte it...

Thanks,
-Chris

 

Hello Chris and Welcome to the forum!

Somebody will be along that will be able to help you out. That is a helpful write-up of what you have tested.

 

Anyone have any ideas, or maybe a wiring diagram for the manual 4WD system?

TIA,
-Chris