I live in cold, snowy NH and have a 1999 F150 AT w/5.4L engine with ‘Electronic shift-on-the-fly’ 4 wheel drive (never had a plow). I purchased it with 280k last spring and am the 3rd owner.

I also currently have a 1984 F250 4x4 with a plow, rear chains and 1500lb weight box that I used to pull the stuck F150 out of a plowed in parking place several storms ago.

I have owned and repaired F250 4x4’s plow trucks (some with over 250k miles) for about 25 years; but this is my first F150.

Latest problem with the 1999 F150 is that 4 wheel drive (and rear limited slip (if it has it)) are not working.
Observations are: 4 wheel drive switch on dash is in 4H or 4L;
Passenger rear wheel slips (on packed snow);
Driver rear wheel does not slip or move;
Neither front wheel slips or moves;
4 wheel drive indicator stays on no matter what
position switch is on 2, 4H,4L.

I’m used to trouble shooting and repairing straight mechanical 4WD systems.

I have a Haynes manual that somewhat covers this truck.

The wiring diagram in the manual does not cover the ‘Electronic shift-on-the-fly 4 wheel drive.

Since my 4WD indicator is locked on and I don’t have 4WD, what turns on/keeps the 4WD indicator?
Is it in/on the ‘transfer case motor assembly’
Is it in/on the ‘4WD vacuum solenoid/switches’
Is it on the 4WD actuators on the front axle
Or ??

I could also use a wiring diagram that covers the ‘Electronic shift-on-the-fly 4 wheel drive and associated parts.

I do all my vehicle repairs outside and can block the F150 totally off the ground once it warms up a bit.

I totally pulled down a 1967 F250 4x4 front axle and rebuilt it in -14f weather after I snapped a shaft plowing years ago.
I’m too old to do that at that temperature again.

Thanks.

 

Double post, oops.

 

If the 4x4 indicator is staying light then the odds are that the GEM is the cause.
The GEM controls the shift motor in the transfer case and the vacuum solenoids on the fire wall that control the vacuum to the front axle actuator motor. When the GEM sees a request for 4x4 it activates the shift motor in the transfer case and the solenoids. It also turns on the 4x4 indicator in the instrument cluster. If the light stays on the GEM is keeping it on even when is should not.

Here are some schematics for the ESOF system.







Some times banging on the shift motor fixes it. If it does replace the motor

 

Look on the door jamb sticker for the axle code. If it starts with a letter you have a LS rear, if it starts with a number it's an open rear. Mine is H9, which is LS. 19 would be open.