First off, thanks for all the great threads on this forum, they have helped me out a ton. I have searched for my issue but can't find an answer.

My 4wd has worked great until a week ago. I started my 2002 Ex 7.3l and pulled out of the driveway. As I pulled out I noticed (felt) that it was in 4wd but the ESOF switch was still in 2wd, as it was the day before when I parked. I tried to take it out of 4wd but the switch did nothing. After a few minutes of driving, 4wd disengaged. Now the ESOF doesn't work.

So far I have checked all the fuses. I tested the two wire connector leading to the transfer case motor and have no power when the ESOF switch is turned. I tested the ESOF switch and the ohms readings were within spec at each position.

What I can't find is the relay box housing the two transfer case motor relays (Auxiliary Relay Box 3, housing relays C1129/K378 & C1173/K379). I have read many forums and threads stating the location is next to the master cylinder. I have seen posted pictures of the location with the relays but my Ex doesn't have them in that location (on the metal holder between firewall and air box). I have also read they are behind the radio, but they aren't there either.

Any help on locating the relays?

 

The ESOF system is a vacuum one. The vacuum solenoid is located near the battery. There is one electrical connector and some vacuum lines going into it. The best way to fix a faulty ESOF system is to disable it. Go buy some aftermarket locking hubs (Warn or Mile Marker. Install them and disconnect that solenoid and cap the vacuum lines. The switch on the dash will still work to engage/disengage the transfer case. When you want 4x4 just manually lock the hubs and turn the switch on the dash. You can leave the hubs locked and the switch in 2wd and drive around no problem. When you want 4x4 you just turn the switch to engage the t-case. This is what I did with mine and it worked great. The factory system that they used on these vehicles was not that good and the hubs were prone to sticking and locking up (always in the wrong state, locked or unlocked, when you didn't want it). Good luck!!

 

The issue I'm having is electrical not vacuum. I have no power going to the transfer case motor. The transfer case has to be engaged in to 4wd before the vacuum system will try to lock the hubs. I always manually lock my hubs just because I dislike the ESOF auto locking hub system.

I still can't locate the ESOF relays. I took the dash apart and they aren't anywhere. The Ford wiring diagram has the relays and box numbers but no location. I will call a Ford dealership on Tuesday to see if they can help.

I'm also trying to find the orange and yellow wires that power the transfer case motor. I thought maybe on my Ex the 4wd/GEM module to the place of the relays, but the module doesn't have either of the yellow or orange wires connecting to it.

My Ex was built late in 2002 so I'm thinking the wiring might different than most 2001-02. Does anyone have a 2002 Excursion with the relays next to the master cylinder? Or have any idea where the relays might be located?

 

This link may help. Also check the tech folder as there is some ESOF troubleshooting guides.

https://www.ford-trucks.com/forums/1...ch-folder.html

2004 F250 Auxiliary Switch Install

 

Ah, sorry about that. It is the GEM that controls all of the 4x4 actions. The gem is part of the fuse box that is by the drivers side foot well. I'm surprised that the relays or the wires were not going into that module. You need to find the correct wiring diagram which you already know.

Good luck!!!