As stated in my recent Hello post, having issues with 4x4 on a 1999 XLT with 4.6 ESOD.
My cousin who backed out of a deal to buy this truck for just the engine told me the GEM was bad so I swapped it out.
Former owner and cousin said 4x4 worked but 4L did not.
After swapping GEMs still no 4x4, had codes P1876 and P1838 so swapped back GEM module since both said 4x4 worked, just low was issue.
Now codes are P1824, P1832, and P1838 and the truck does not care if seatbelts are connected or not...
I tested voltages to 2WD and 4WD solenoids, both have power, but both also have ground, no matter position of the switch on dash, indicating a short to ground.
I also tested both solenoids to see if they were each trying to send vacuum down to front axle and only the 2WD solenoid passed vacuum, the 4WD did not, prob lucky there..
So I know I need a new solenoid for 4WD, and I do have a spare shift motor for transfer case, cousin who gave it to me mentioned something about having to pull apart connector and push 1 pin into it from transmission, I sort of forgot, think P14, but certainly can compare when swap motor.
Question, can this transfer case motor cause any of the issues with shorting the trigger grounds for the front axle solenoids, I know there is some plate inside that send a position signal back to GEM.
The manual I bought online is lacking all schematics, just troubleshooting steps, and since this truck is a real joy to get up under dash to disconnect GEM harnesses n test, almost ready to get cutting tools out and making a huge hole there so can do this, thought ask if motor could cause this before I get creative in trying to determine if GEM or harness is suspect here...
I see I am looking for C3-2 605 red for the 4WD signal and C3-7 145 GY/BK for 2WD signal, but wasn't sure which of the 3 harnesses were considered the C3 harness to pull..
I have all summer to get this done, well 3 months until chance of snow again up here, so back willing, will try and get this sorted before that time.
So have known good shift motor and ordered a solenoid to at least replace the known bad parts, just need info on this short to ground issue.. thanks...

FIXED, was transfer case motor, cheap Amazon motor cured my issues...

 

I see post with comment about how the T case motor controls those ground feeds through the GEM to those solenoids on firewall.
"The firewall solenoid is supplied ground from the Gem 'through' the case motor circuit board."
The motor under this beast is so rusty and deformed looking, I can see it being the root of all evil here..
I have a spare motor so will swap that tomorrow and try to figure out the moving of 1 pin from some speed sensor into harness of replacement motor.
And ordered the solenoid, updated revision, for the front axle so will keep that unplugged until that part comes in case it has internal short, did not get meter out, was using test probe that reports voltages n if power or ground or open you are probing..
Both previous owner and cousin claiming the 4x4 worked just a few days earlier with a bad solenoid makes no sense to me unless it decided to fail after I nabbed it.. anyhow will update, and read any replies, thanks..

 

Side note: Ticks are out up here, already had deer ticks, dog ticks, and lonestar ticks on me this spring way up north here.
As a longtime sufferer of Lyme disease and having had the alpha-gal syndrome for 3 years, be on the lookout for these pesky fiends.
I lay on tarps with cardboard over and still have to pick a few off me every day..
They can be nearly translucent first year, tny as spec of finely ground pepper and dark 2nd year, and still very small as an adult 3rd year on..

I made a homemade repellent using cedarwood oil and few other essential oils to help with skeeters, jiggers, n all the other pests in the woods up here, just need to get on making fresh batch..
for the yard, 1oz of cedarwood oil per gallon of water in sprayer can do a large area, I can do all the trails n edges of all openings with just that gallon per acre and can smell it on those humid mornings like living in a cedar grove.

Only thing hate about the woods.

 

Forgot to mention I have the top relay removed from under dash panel, the delay relay think it is, otherwise fuse 14 pops and lose power windows..
Only side effect I see was the interior lights do not work., maps still do though which is fine for me.. in case related to any issues I am having.
It is a short to ground issue as well.
This truck is badly rusted on rockers, enough so that a red squirrel got inside and chewed hole into headline and made nest under passenger seat in the 4 years it sat idle, will pull that panel off over glovebox to expose relays and make sure it wasn't up in that area, I did not see any signs of it going that direction, but mice may have and made a mess up there,.. could hear solenoids up under dash on 1st attempt at going into 4x4 mode, it will do it once each time battery disconnected for 15m or more, then silence aft it realizes nothing working ??

 

Well I read dozens of posts and copied a lot of the answers to give me some steps to take tomorrow, weather permitting..
Will unplug T case motor harness and see if the grounds are still active, if they are check for pinched wires,.
Have spare motor so can test traces on the wiper inside and compare to unit in truck now, as stated though I would be amazed if it worked, it looks like the field collapsed from the housing rusting out and not supporting the magnets..
I mean I will post some pics of it, looks like was bottom of ocean for decades., this NW WI salt really eats the vehicles up.
I did field engineer work for IT for years, the Buick dealership stated they had frames rusting out in 1 season from the salt. like dunk that subframe in the paint they use for ocean liners, come on Buick.,,.lol

 

Mother was sick today so only got to do few things.. swapped in the known good T case motor, moved the 1 wire into harness.
No change in operation, wasn't expecting much with possible bad solenoid for 4x4..
Got the meter out and checked ohms at those solenoids. 72 ohm across contacts,
Key off they both had 45k ohms on ground leads.
Key on 2wd switch on 2wd solenoid 0 ohm, 4wd 7.4k ohm, I did hit 36 ohm few times on 2wd, likely small amount corrosion on contact.
Key on 4wd switch on 2wd solenoid 36 ohm, 4wd 7.4k ohm
Key on 4L switch on, 2wd solenoid 36.7k ohm, 4wd 7.4k ohm again...

So the 4wd negative only changes key off and the 2wd does not really disengage until in 4L...
I did not check sweeps in newer motor, at least that one is not caked in rust and the screws look like new, have set of security bits to remove it if this is next step...
Did not pop dash cover off to inspect wiring,
Replacement T case motor was in slightly different position and had to rotate shaft on case to align to assemble. maybe 5-8 degrees or so.
Old motor had popped screws holding motor to gear reduction head, just corrosion kept it together.

Will check fuses 6-8-15-20 for corrosion, saw 1 post resolved with cleaning of the fuses..
Any other suggestions, my mind is a little F'd from this Lyme and was forced to retire, but was troubleshooting tech for decades, degree in electronics, Physics, Broad Field science, Computer networking few others, school was close and loved to learn until could no longer read...
I will get there...

 

Had a chance to hook up scan tool anyhow, 2 new, 2 old and 1 gone after motor swap.
Now have P1824, P1876, P1838, and P1867...
I saw posts where they commented on cleaning sweeps on motor, on both of mine that is a blue sealed unit, are you guys taking that apart somehow?
Will see if get time to unplug motor and check grounds again, not sure if this 45k ohms is bad or not, would think infinity would be better reading.
My cousin is 'swap the GEM swap the GEM, it is always the GEM', I already swapped it once, swapped it back, and hoping not a 3rd time...

Can hear center solenoid click few times, the ones over glovebox do nothing, and no wires chewed up with visual inspection.
Nearly every fuse had some old dielectric grease that dried up, made contacts have caked tan coating, removed all of that on fuses.

 

Found this page with lot of info on this transfer case and its operation, guess will search there for help too..

https://ricksfreeautorepairadvice.co...transfer-case/

 

Found a new shift motor for 55 going to try that next, just toss parts at it..
Did not see any damage to any harnesses, appears the one to motor goes under driver seat down through cab and did not feel like trying to take off seat to access wires..
See if I fall down the rabbit hole on this truck, had hoped to hear someone chime in with similar issues, guess everyone hunting wabbits..

 

I think you are going to have to chase wires and grounds.

 

The only thing missing, which is what I need the most now, is the schematics.
I have nothing on wiring or where harness are located to do any troubleshooting.
I have Full Ford manuals on 2002 Cougar if anyone wants to trade, series of 3 thick books...
Used to have a 02 Cougar ZN, traded it for a 69 Buick California GS..

 

This might help. I don't know if it's that detailed but it's worth a try:

https://drive.google.com/file/d/1-4d...ew?usp=sharing

 

Most excellent, I had a full manual but for some reason that whole section was missing, thanks much...

 

*******FIXED******

Transfer case motor was issue, now have all options functioning, 4x4, 4Low..