I have a 99 3.0 4x4 as the title states and my 4x4 won't work. I noticed that the vacuum lines are not hooked up and some of the ones that route directly on the frame to the axle hub are bypassed by another hose.

Does anyone have a diagram of the vacuum lines? I've even called the Ford parts department and the guy couldn't find any vacuum lines for the 4x4 to help get me started.

I do have the 4x4 hi and lo light flash 6 times every so often. When I turned the 4x4 switch I also hear a clicking. My first step is to get these vacuum lines for the hub lock hooked up properly. I'll then troubleshoot from there.

Any help with these lines would be greatly appreciated. I'd even be willing to pay someone for their time if they took some pictures/videos of theirs and how they're routed.

 

Welcome to the Forum

1998 to 2000 Rangers used Pulse Vacuum Hubs(PVH)
These were a bad idea and Ford started changing over to Live Axle(always locked) front hubs as early as late 1999.
2001 was first full model year with all Live Axle Hubs

Fixing the PVH system can be done, changing them to manual hubs would be time better spent.

Troubleshooting PVH article here: Ford Ranger How To: Troubleshoot/Fix Your PVH Hubs (1998-2000)

Switching to manual hubs seen here: 1998-2000 Ford Ranger Rugged Ridge (AVM) Locking Hubs

The PVH system just locks or unlocks the front hubs

In 1999 Ranger the 4WD buttons control the transfer case shift motor via GEM(generic electronics module)
1999 4WD Wiring diagram below

Basically it works like this
Inside the shift motor are 4 contacts on a wheel that turns when the shift motor turns.
These contacts open and close as the wheel turns to the 3 transfer case positions, 2WD, 4hi, 4low
So each position has a set open/closed contact "map", thats how the GEM can tell what position the transfer case is in.

GEM runs a double relay box that sends 12v-ground to shift motor, or ground-12v, so just like power windows work, polarity is reverse to roll window up or roll it down, same for shift motor to turn it clockwise or counter clockwise.

So GEM "knows" what position shift motor(transfer case) is in by the contacts
And it can power up and turn the shift motor to one of the other positions, power it until contacts are correct for that position.

The buttons on the dash go to the GEM, inside buttons are 3 resistors, GEM sends buttons 5volts, if it gets back 3volts it select 4hi, 4volts 2WD, 2volts 4low, just examples
If shift motor moves to correct position for 4High then GEM will turn on 4high dash light, same for 4low, if motor is not moving to correct position 4WD lights will flash.

The "clicking" you hear are the Motor relays, so GEM is activating the motor, but flashing 4WD lights would mean motor is not moving, contacts are not changing.
If it was functioning correctly you would hear the click of the relay, then a second or two later the 4high light on the dash would come on, if shifting from 2wd to 4wd, the second or two delay is because GEM doesn't turn on the 4wd light until contacts confirm correct position.

Shift motor rebuild or swap, read here: How to: Rebuild 4X4 Shift Motor | Ford Explorer and Ford Ranger Forums - Serious Explorations

You can see whats what like the contacts and contact wheel, also the 3 positions of the transfer case



In 4WD GEM activates vacuum switch sending vacuum to PVH system

 

Thanks for the welcoming! This is excellent information. Thank you for taking your time to write this up. After I get home today, I'll go through everything and give an update on my progress.

 

I'm finally getting around to checking the 4x4 with the help of RonD's post. I started by looking at the wiring diagram and begun at the 4WD mode switch to test the resistance of the switch and all seems well there. When I toggle the switch I hear clicking and the lights on the dash flash. I decided to move on down to the transfer case shift motor and test for power. I tried to test each of the 8 pins and got no power at all. There was some current around .05V. Let me note that I had tested for current with the car running and in park. Does the brake pedal have to be pressed in order to get current to any of those pins?

This is where I had stopped troubleshooting as I wasn't sure what else to do other than try to find the fuses/relays. It also seems that there are two modules (electric shift and the GEM). Where should I go from here?

 

The GEM controls the 4x4 shifting
Shift module is just 2 relays in a box, and if you hear a "click" then the relay is working

4WD Lights on the dash Flash because shift motor isn't moving after relay Clicks
Contacts are most likely just Grounds so no voltage, but never test one

Tap on the shift motor with a hammer, and see if it starts moving, motors brushes are usual problem, they get stuck from disuse so no contact with rotor

GEM is behind the Radio
Listen for the "Click", shift module could be there as well

Bulk of the wiring that comes from shift motor goes to the GEM, so locating shift module near the GEM would make sense, but car makers rarely think that way