4wd won't engage

[Cooper68]

I just bought my first 4x4 truck so I'm really new to the 4wd system. Right now my lights don't come on while the truck is running, but if I leave the switch in The 4wd hi/low position and then turn it off and back on the lights come on but the 4wd still isn't engaged. Ive checked all the fuse that I think have to do with the 4wd system but they all look fine. It's a 1998 ford ranger xlt

 

[RonD]

There are 4 fuse involved counting the Brake Light fuse.

Fuse #3 in the engine fuse box powers the shift motor on transfercase, 20amp

Then fuse #26(10amp) and #27(15amp) in the cab fuse box

Fuse #9 is the Brake light fuse

1998 Rangers used Vacuum activated front locking hubs, PVH, these worked when new but had problems as they aged, Ford only used them for 2 or 3 years then just Locked the front hubs permanently and called it Live Axle.
read here: http://www.therangerstation.com/tech_library/troubleshoot-fix_pvh_hubs.shtml
here: http://www.therangerstation.com/Magazine/Apr04/offroad.htm
And here: http://www.therangerstation.com/tech_library/AVM_hub_swap.shtml

The electric shift motor on transfercase or 4WD shift module could also be the issue.
4WD shift module(electric shift control module) is just a box with 2 relays inside that send power to electric shift motor, one for turning motor clockwise the other for turning motor counter clockwise.

The shift motor can become inactive if not used every month or two, the brushes that power the rotor lose contact inside the motor, try tapping on the motor a few times then see if you can shift into 4WD high and back to 2WD.

Here is the 1998 4WD wiring diagram
EDIT, look here for wiring diagram, 4th post: http://www.therangerstation.com/forums/showthread.php?t=162915