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Discussion Starter #1 (Edited)
This is a revisit and updated version, with new pics, of the original “E-Lock in 2WD, 4HI and 4LO” mod done back in 2005. Credit for discovery, initial write-up and execution of this mod goes to Austin, and can be found HERE in his original thread. Thanks goes to him for making this possible for us all.

Due to the # of people who seemed to be having issues or were hesitant to attempt it on the ’08-present models, and the lack of recent photos, I decided I’d give it a shot on my 2010. After one failed attempt due to a crossed wire and blown fuse, and then it acting weird on me, I was able to get it to function as desired. If you have basic mechanical and electrical skills you should have no trouble accomplishing this. Just be patient and take your time. I tried to be as clear as possible, but if you are unsure of something just ask.

DISCLAIMER: By doing this, you are assuming all responsibility and/or liability for any damage that could result due to your work or driving practices after completion, as well as any issues that may arise with warranty work should you break something and they find this done. Not all service dept's are ok with us doing stuff like this

List of items you will or may need to do this:
• DPDT relay (Radio Shack PN: 275-218)
• Various wire connections. (I used bullet connectors. Get at least 8 pairs)
• Wire Taps (unless you choose to strip and solder those connections)
• Spade terminals (8, 3/16” females for the relay terminals, and whatever you need for your switch)
• Heat Shrink Tubing (if you want it)
• Test light (to verify 12v switched source if you want)
• Multi-Meter (good to have for any electrical work and for checking continuity, voltage, etc…)
• Wire (I used 16g)
• Wire cutters/crimpers/strippers
• Whatever you need to remove any paneling or seats if needed
• SPST (on/off) Toggle switch, unless you choose to use factory switch; see the update below for this

Terms:
DPDT: Double Pole Double Throw
DLCU: Differential Lock Control Unit
DLS: Differential Lock Solenoid

NOTE: I am not sure how the VDC, ABLS and ABS functions on older models, but on my 2010, when I flip my switch in 2WD, the “VDC OFF” light comes on along with the “DIFF LOCK” light.

UPDATE: This can now be accomplished using the factory diff lock switch to activate the mod. CLICK HERE to learn how. If you choose to do it this way, leave out the wires that would go to the toggle switch and follow the directions in the link.


After reading everything in the original thread along with comparing new and old wiring diagrams and schematics, it appeared that the function was the same, and things didn’t look different from an electrical standpoint. I started by locating the DLCU and verifying that the wire colors and terminal locations were still the same, which they are. The DLCU on my 2010 PRO-4X CC is located on the back of the cab under the carpeting behind the passenger side seat as shown in the photo below. It may differ between CC and KC or even trim level, but my guess is it will be behind the seat somewhere. It will have a big “D” on it just as the one in the original thread appears to.



From here, I located the wires needed based off their location on the connector. The picture below is looking at the plug from the side the wires go in (the “Harness Side”, or HS, is how the service manual refers to it).



The next diagram is how the terminals are numbered looking from the Harness Side and I have colored the terminals you need, based off the color of the wire coming out of them. These are the wires we need to locate in the kick panel.

NOTE: You can do all the wiring for the relay back here behind the seat if you wish. This will eliminate all worries about choosing the correct wires from the bundle up front. All you will need to run to the front is 2 wires to your switch. The actual wiring directions are the same regardless of where you place your relay, so long as you use the correct wires. If you choose to do it back here, just follow the steps for cutting and tapping wires as described later on.

DLCU Connector (looking from harness side)



Next, I traced the wires from the back up to the kick panel using a multi-meter. There is several of each color mixed in the wire loom running down the truck, so you need to be sure to remember which ones you choose.

The next photo shows the location of the wires you will need almost exactly as they were in the loom. The blue wire was the only one I moved to get a picture of. The Black, Yellow and Purple wires all pass through the connector in the white box and then up and to the left in this photo. So you can verify the correct wires by making sure they go there as well. The blue wire goes up towards the firewall with some others.



Next is a shot of the wires separated from the rest.
The blue wire is a shade darker than the other blue wires and they are all just a bit bigger (16g vs 18g).
The blue is an ignition-switched +12v source.
The black is a ground
The yellow is a switched 12v from the DLCU
The purple is a switched ground from the DLCU.

 

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You're an animal!!!:D Great job!!!!!
 

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Discussion Starter #3 (Edited)
NOTE: For the purpose of hooking things up, “DLCU side” refers to the side of the wire running back into the loom to the rear of the truck. “DLS side” refers to the side running towards the firewall.

Cut the YELLOW wire (from terminal 12 of the diff lock control unit (DLCU) harness).
Cut the PURPLE wire (from terminal 11 of the DLCU harness).
Tap into the BLACK wire (ground) (from terminal 3 of the DLCU harness).
Tap into the BLUE wire (from terminal 1 of the DLCU harness).

The next photo shows the wire loom cut back, the yellow and purple wires cut, connections added to them, and the blue and black wires with taps on them. I made sure to use opposing connections on the yellow and purple so that they could be plugged back in to function as factory, yet could not be accidentally crossed to each other. The taps I used will accept a male spade terminal which you will see in another photo. I also used heat shrink on all connecters to give it a finished look and keep it protected.



Below is a picture of the relay with pigtails added to all the terminals. I labeled them all so it would be easy to match them up since I only had red and black wire. The connections that will go into the wire taps have 2 wires each coming out of them. Make sure the wires are all long enough to reach their respective locations. Also, make sure to use the correct ends on the leads so that they match up to the connectors you put on the vehicle-side wiring.



Connect DLCU side of YELLOW wire to relay terminal 1.
Connect jumper from BLUE wire (power) to relay terminal 3.
Connect diff lock solenoid (DLS) side of YELLOW wire to relay terminal 5.

Connect DLCU side of PURPLE wire to relay terminal 2.
Connect jumper from BLACK (ground) wire to relay terminal 4.
Connect DLS side of PURPLE wire to relay terminal 6.

Connect jumper from BLUE wire (power) to the supply side of rocker switch.
Connect the other side of the switch (labeled “earth” on mine) to ground.
Connect jumper from load terminal on rocker switch to relay terminal 7.
Connect jumper from relay terminal 8 to BLACK wire (ground).

NOTE: If you choose to use a switch w/o an l.e.d., there will be only 2 connections on it. One will receive the power and the other will connect to terminal 7 on the relay.

Here is the diagram for the relay and how you need to hook everything up.



Below is everything all hooked up as it should be. The two wires running down and out of sight are for my switch.
Once you get to this point I would suggest testing it before closing everything back up. Once you verify it will work, the relay will fit in the space by the brown plug, and all wires can be neatly tucked out of the way.



Feel free to ask any questions, or point out any mistakes, and I will answer them to the best of my ability.

ENJOY!

I have verified this works by switching it in 2WD, 4HI and 4LO and both on pavement (in 2wd only) and dirt up to about 25mph. You will get a "diff lock" light on the dash and on my 2010 at least, the "VDC OFF" light as well.
 

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There is 2 more then!!! :)
 

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Discussion Starter #6
Just an FYI for anyone who attempts this. I had some issues after getting it hooked up and working. On the way to work I was playing with it and it seemed to work intermitently, then not at all. I rechecked it all, then tried again, with similar results. I unhooked everything, put it back to stock and drove around and cycled it with the stock switch in 4lo which worked, then went back and hooked it all up again. After driving around some more I played in a dirt lot using both switches in all modes and all seems well now. I'm thinking that the system is either very sensitive to voltage change (since yesterday just a test light would cause it to shut down, and I sat for quite a while today with ignition and lights on) or that it is finicky until things warm up. It also may take a few feet of driving or slight turn of the wheel to lock up and unlock it. If you follow the directions I posted then the wiring should all be good. If you experience any issues, give it a while of driving before trying it again just to be sure it wasnt something like I experienced. If in doubt, double check everything. And don't hesitate to post up any questions as I'm sure if I can't answer, someone else can. I try to log on at night to reply since I cant post from work.
 

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Awesome Job Irish! Looks like the new model T's will be able to launch in full time rear wheel spins!!! It's great for playing in the dirt and mud... and hitting the trails when you don't want to run in 4LO but want extra traction... In fact, I can't even remember the last time I used 4LO since I did this mod... just keep it in low gear and pulls great!
 

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Very nice writeup!
 

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Discussion Starter #11
I've made some observations while using the new mod. Although my VDC OFF light comes on with the DIFF LOCK light, VDC still seems to be enabled since when I had it locked and went into a slide on a turn while spinning the wheels it quicky tried to use the brakes to straighten me back out. I am able to spin both rears in a straight line with no SLIP light or throttle override. With the diff locked in 2wd on a dirt road I switched the factory switch and the ABS and SLIP lights came on as well. I slammed the brakes and it seemed as though the ABS was in fact turned off. I think my relay may be touchy, and I may replace it, since the diff won't always lock with the first flip of the switch. Also it sometimes takes a slight turn for it to disengage.
 

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let me know what you find out, im interested in doing this, just gotta make sure I hide it very well. I might just do everytihing in the back and run the switch up.
 

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Discussion Starter #14
let me know what you find out, im interested in doing this, just gotta make sure I hide it very well. I might just do everytihing in the back and run the switch up.
Doing it back there would eliminate any uncertainty of wires for sure. Then just run 2 wires up to a switch and your set. Only drawback is you've got to remove the seats and it's a pita to get to should you ever need to work on it.

But it will definitely be out of sight.
 

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I've made some observations while using the new mod. Although my VDC OFF light comes on with the DIFF LOCK light, VDC still seems to be enabled since when I had it locked and went into a slide on a turn while spinning the wheels it quicky tried to use the brakes to straighten me back out. I am able to spin both rears in a straight line with no SLIP light or throttle override. With the diff locked in 2wd on a dirt road I switched the factory switch and the ABS and SLIP lights came on as well. I slammed the brakes and it seemed as though the ABS was in fact turned off. I think my relay may be touchy, and I may replace it, since the diff won't always lock with the first flip of the switch. Also it sometimes takes a slight turn for it to disengage.
I'm thinking that your observations are not limited to your mod. I've had issues with the differential locking/unlocking and I have yet to do this mod.
 

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Doing it back there would eliminate any uncertainty of wires for sure. Then just run 2 wires up to a switch and your set. Only drawback is you've got to remove the seats and it's a pita to get to should you ever need to work on it.

But it will definitely be out of sight.[/QUOTE]
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If I set the relay in the back, wouldnt I need to run 3 wires if I wanted a lighted switch? BTW. Thanks for posting this mod. You and Austin saved me some $$.
 

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If I set the relay in the back, wouldnt I need to run 3 wires if I wanted a lighted switch? BTW. Thanks for posting this mod. You and Austin saved me some $$.
Nope...your third wire from your switch is for the switch's illumination ground...ground that sucker anywhere under the dash...
 

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Discussion Starter #18
Nope...your third wire from your switch is for the switch's illumination ground...ground that sucker anywhere under the dash...
Mine ground for the switch is temporarily just attached to the screw that holds the panel on by the OBD plug. I may just put in a small metal toggle with no led somewhere out of sight of curious hands since with the lights on the dash I really don't see the need for another light and big switch for someone to question.


So far aside from the thing not always engaging on the first, or 2nd, or 3rd time, I've had no other issues and have run it up to 60mph in 2wd and about 50 in 4hi. I still think my relay is on the fritz so I may just replace it when I have time.
 
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