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No 4WD and no dash light

38K views 48 replies 4 participants last post by  tykesplace 
#1 ·
I'm sure this is related to the issue I had this summer when my trans/transfer case wiring harness dropped onto the front drive line while my hubs were stuck and the harness got torn up. Yeah it was a ****ty day. Anyway I cleaned it up, soldered in, and shrink tubed the wiring repairs. I'm feeling confident that the wiring repairs are good. It was summer and I didn't think about checking the 4wd.

Well now it's snowing and I find that I have no 4wd. No light on the dash even. I understand about checking the t-case motor for voltage, but if that's the problem should the dash light still work? I replaced the two under-hood relays in July, and the fuse is good. But some of the wires did short out to the truck. Maybe the wires shorting out fried a relay, the motor, or the GEM? Just wondering before I start replacing stuff, what component could have gone bad that would make the dash light not work?

Was going to go hunting this weekend too. Might have to skip that.
 
#32 ·
It's probably not the gem, I've had the same problem on two different trucks.
The relays for the esof are always powered and the gem provides ground when you want to shift.
You'll need to remove you driver's side fender liner and open up the wire harness going from the relays to the gem, look for a brown wire with a white tracer and there's more than one.
I don't know why but they go green and stop communicating ie providing ground via the gem. Must be bad wire insulation or they get damaged during instalation.
Here's what I found in my trucks.
 

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#33 ·
Thanks moose. After my testing today that's going to be my next wire to check.

I fully checked the relays today. I found that the one closest to the fender is the H2L. Following the diagrams on the relays I applied power across pins 85 & 86 and confirmed the relays operate. Next I looked at their connections to the t-case motor. At rest the relay pins 30 & 87A are connected and go to ground. When a relay switches it connects 30 to 87 (hot) and completes the circuit to power the motor. So I pulled the relays and connected the corresponding harness connections with patch wires. If I connect 30 & 87 on the H2L side the motor engages. Put the wire back and connect 30 & 87 on the L2H side and it disengages. I'm not sure but by doing this manually I might be going right by 4H to 4L. With the key on, in neutral, and brake applied the above tests are the same. Meaning the H2L test doesn't "turn the motor more". I can roll the truck a bit though and confirm the front driveline moves though. Test L2H and its free. Tomorrow I'll test drive and see if it's going to 4L.

I also pulled the dash switch. Not sure what to check on the switch itself, but I took it apart and it all seems intact. It's light gets power. Operating the switch makes connections through resistors(?) in the switch between the DB and W/LB wires, which go to the GEM. Checking resistance in the the switch as I move it through 2H>4H>4L I read 3.9, 1.1, and 0.356 respectively. Don't know if those numbers are what they should be. Manually patching the DB & W/LB wires has no affect.

So after all that I'm going "upstream" tomorrow. It seems after the relay tests that the relays aren't getting their "switch on" signals from the GEM through the O/LB and BR/W wires. So I'll check their continuity to the GEM. I'll also check the DB and W/LB wires between the dash switch and the GEM. If that doesn't solve things I'll open up the harness underneath where I did all my patch repairs. I think that harness goes to the transfer case, GEM, and DTR sensor.
 
#34 · (Edited)
So today I took apart the wiring harness to the trans and t-case so I could see wire colors. I re-checked continuity of the wires between the GEM and the plugs, checked my wiring repairs, the relays, fuses, dash lights. Put my original GEM back in. Still no 4WD. I'm at a loss.

Rather than describe the wires I checked, I've highlighted them on the diagram in green and attached it here. Hopefully you can read it. If a wire color indicator isn't highlighted I didn't check it, probably because I don't know where it is.

I'm wondering about the thing on the t-case that the 6-pin connector goes to. Could there be something in there that fried? Position sensor or something?

Maybe I need to just pay the dealer to diagnose it.
 

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#35 ·
That pink/orange ground wire from the position switch could be the whole problem if it isn't connected to ground. Could be the wire that completes all the circuits to the position switch. Shouldn't be that hard to check. Just probe that pin on the connector with your other probe on any grounded part (frame, etc.)
 
#37 ·
It says x4 Ground on the diagram. Where does it come from on the t-case?
Sorry, can't help with that. I don't have one to look at.
I just learned that there are differences in the 99 wiring diagram I posted and other years up thru 01 models. I checked the equivalent diagram for 01 and 02 trucks and there's no pink/orange wire there. The ground from the switch should be thru terminal 4. If you got continuity to ground there thru the tranny position switch, then I'm as stumped as you are.
 
#39 ·
I did a quick search on Tousley's site and also Fordparts.com and couldn't even find the shift motor. I don't know whether the position switch is only available with the t-case motor or separately. I'd suggest a call to Tousley if you're looking to replace it. My service manual doesn't give a troubleshooting guide for the t-case position switch like it does for the ignition switch and other similar components.

Sorry I couldn't be more help.
 
#41 ·
Yep, they're a site sponsor and sell parts at discount prices thru their web sales division.
 
#42 · (Edited)
Transmission Range Switch - not for the T-case
 
#44 ·
Sorry, that's not it. That's the DTRS (Digital Transmission Range Sensor) that goes on the transmission. Rockauto listed it under the Transfer case. The search goes on.
 
#45 ·
I took the truck to another dealer yesterday. Small town type place so they were willing to work with me. Tech spent 3 1/2 hours checking stuff but they only charged me for 1 1/2. I even spent some time under the truck with the tech going over stuff. He's convinced it's a ground issue with the GEM. With his service computer hooked up he could read the signals for 2WD, 4H, and 4L when the switch is turned. He confirmed my wiring repairs were good. Even said he'd bring me in if he needed a wiring harness rebuilt because mine looked factory after I was done with it. :thumbsup:

What he was concerned about was getting resistance (rather than 0 ohms) on the P/Y wire between a good ground and the T-case, GEM, and DTR connectors. We're also getting some continuity between the P/Y pin on the DTR connector and some of the wires on the DTR harness. He doesn't know if that's the problem but he doesn't think those wires should be getting ground. So klhansen, do you also have a diagram for the DTR part of the system? That's connector 1012 according to the diagram. I don't think I can pull this entire harness but if I can isolate it at the connectors, I can start a process of elimination to find where I'm getting grounded.

BTW, that x4 Ground on the t-case diagram? He also doesn't know what or where that is. Even his software shows it and it "updated". He thinks it's a mistake.
 
#46 ·
Here's the diagram for the DTC connector.

Text Plan Diagram Floor plan Technical drawing


Hope you get it figured out. Sounds like your guy may be on the right track.
 
#48 ·
Sorry, I read "DTC" when you said DTR. [smacks forehead]

Here you go.

Text Line Circuit component Diagram Parallel
 
#49 ·
So I last posted on this thread over a year ago. Over the summer I checked everything I could think of, with the help of this forum. I tried a new computer, but that's not it. I can bypass the shifter relays with a wire and shift the case, so I know the NP271 motor and wiring harness is good. I took apart the dash switch and checked everything there. I checked continuity of every wire I could trace from the diagrams. I also took it to two mechanics and spent about $300 in shop time diagnostics. It's stil not fixed. :icon_mad: They think it's a ground issue but we can't locate it.

So here's what I'm considering, and I'm hoping someone here can tell me that it will work. I can get an NP271 (manual t-case) from a salvage yard. They open it up to check the internals and install a new seal kit. I can also get the linkage, shifter and boot. With shipping and core return it would cost me about $550 for everything.

I think the NP271 will mate to my 4R100. But does my 1999 F350 Crew Cab with NP273 already have the mount points and such for the manual linkage and a knockout for the shifter? Has anyone done this conversion before that can give me some advice?
 
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