Following information credit given to & written by: Hoaiphong Truong

   Retrofit Electric Locker  




  The Toyota electric-locking rear differential is one of the most coveted factory options in the off-road community.  Imagine an instant spool at the touch of a button on your dash.  Unfortunately for me, my 2000 4Runner didnít come equipped with one, even though it was an available option at the time of purchase.  For those of you unfamiliar with what a locker does, I recommend reading Lars Dennertís article on Traction Aiding Devices. The way I looked at it, I had two options:  trade in my current 4Runner for a locker-equipped 4Runner, or find a way to retrofit a locker into my existing rear differential.  Trading it in was out of the question since I would have had to take a huge loss, so I began looking for ways to retrofit one into my 4Runner.



  I began by doing some research and what I found was that my 4Runner was partially pre-wired for the electric locker.  The Locker ECU harness/plug was hiding behind the driverís kick panel.  I then removed the dash surrounding the steering column and found the plug for the RR DIFF LOCK switch.  At that point, I was ecstatic.  Unfortunately, the excitement was short-lived, for thatís all the pre-wiring Toyota felt compelled to do on my locker-unequipped 4Runner.


  After spending half an hour at the Toyota parts department, I was able to conclude that all 3rd generation 4Runners came with one of three different main electrical harnesses from the factory (NO ABS, ABS, and ABS+LOCKER).  By main electrical harness, I mean the large bundle of wiring that runs the entire length of the body.  The factory locker wiring is an integral part of this main harness, and it would have cost over $200 alone to change my ABS harness to the ABS+LOCKER harness.  Since this was already cost-prohibitive (not to mention labor-intensive), I abandoned the ďtotally stock wiringĒ idea.  Hereís how the main electrical harness differs on ABS and ABS+LOCKER vehicles (Thanks to Eric Clayton for the ABS+LOCKER picture).

ABS left, ABS+LOCKER right. 
Notice the ABS+LOCKER harness has a lot more wires.

  Despite the minor setback, I ordered the Locker Harness (Toyota Part #82127-35100), Locker ECU (Toyota Part #89533-35070), and RR DIFF LOCK switch (Toyota Part #84725-35010) anyways.  Whether or not you do your own custom wiring, the locker harness is a must-have.  This harness plugs directly into the differential locker, the plugs have O-rings on them, and it even comes with a breather tube for the actuator motor (which I chose to lengthen and run inside the body).

  When the parts came in, I went ahead and plugged the ECU and Diff Lock Switch into their corresponding plugs.  I placed the transfer case into 4LO, and pushed the RR DIFF LOCK switch in.  Instantly, the previously dormant RR DIFF LOCK light in my gauge cluster began flashing.  This light should remain solid when the locker has successfully locked, but since I hadnít hooked up the locker yet, the flashing was ďnormalĒ.

  At that point, I started looking over the locker electrical wiring diagrams that Dandeman was kind enough to scan for me.  According to the diagrams, all I had left to do was to extend six wires from the locker to the ECU.  Iíve summarized the connections in the following table and diagram.  It doesnít get any easier than this.

Pin # assignments (looking at plug on ECU):

(4)  (3)            (2)  (1)


(10) (9)  (8)  (7)  (6)  (5)


Pin# (on ECU)

ECU wire color

My wire color

Diff. Harness wire color



Light green


Light green



Light green / red


Light green / red



Light green


Light green / yellow



Light green / black


Light green / black



Blue / yellow


Yellow / blue





White/black (2)

Colors:  main color / stripe color

  For future convenience of removal, 6-conductor male/female Radio Shack Molex power plugs were used between the differential harness and my custom wiring.  My wiring enters the body along with the ABS and gas tank lines (similar to the factory-equipped 4Runners).  There's a panel hidden under the rear driver-side passenger seat that's held in by three screws.  When the panel is screwed in, it pushes down on the rubber grommets and forms a nice seal.

  I started by cutting the M1, M2, REL1, and REL2 lines about three inches down from the ECU.  I then soldered the ECU ends to my Green, Red, White, and Black lines respectively.  I had originally used butt connectors, but they gave me an intermittent connection.  I strongly recommend soldering the connections.  The RLP (locked detection) circuit works in conjunction with the ABS ECU and therefore, should not be cut.  Instead, I exposed a ĺĒ section of this wire by carefully cutting off the insulation.  I then wrapped my Blue line around the exposed section of the RLP line and soldered it.  Both ground connections were combined, and grounded to a grounding point behind the driver-side kick panel.  Presuming you are partially pre-wired like me, all other connections should remain intact.  Here's a picture of the connections I made.  I've since gone back and soldered all the connections.

  I then mounted the ECU using the attached bracket to the factory location (there's a designated spot for it!) and a M6x1.00 screw.

  Here are scans of the factory locker electrical diagrams (courtesy of Dandeman) for those of you who aren't as lucky as me to be partially pre-wired.


  Disabling ECU Safeties
  The locker ECU comes with two built-in safeties.  One safety requires you to be traveling below 5mph for the locker to engage (once engaged, there is no speed limit).  The second safety requires you to be in 4LO.  To disable the 4LO safety, you have to cut the '4WD' line, which is pin #8 (blue/red) on the ECU, and ground it.  The locker will now work in 2HI, 4HI, and 4LO.  To disable the 5mph safety, you do the same thing, but with the 'SPD' line, which is pin #10 (green/orange).  I chose to disable the 4LO safety while leaving the 5mph safety intact.  Refer to the previous diagrams for pin locations.


  Lighting the RR DIFF LOCK switch

  For some reason, Toyota chose not to wire the two lines necessary to light the RR DIFF LOCK switch.  Apparently, they did on the Tacomas, though.  Lighting the switch is simple enough to do, but the trick is finding the terminals that go inside the switch connector.  Macgyver was lucky enough to find some of these terminals while rummaging through his local Toyota dealershipís parts bin.  To date, I have been unable to find these same terminals anywhere else.  Pins 2 and 3 are for lighting the switch (Pins 1 and 4 are for locker activation, so the two pins in between are 2 and 3, respectively).  Polarity is arbitrary...  One pin should be wired to either your parking lights for full brightness, or your dash lights if you want to be able to adjust the brightness through the rheostat (interior light dimmer).  The other pin is wired to ground to complete the circuit.


  Bench Test
  Here's a video of the locker engaging and disengaging.  If you listen closely, you can hear the motor.  Very cool!

locker.wmv (375KB)


  Differential Housing Modifications

  The Toyota electric locker comes in three configurations:  4.10, 4.30, and 4.56, which covers all the gear ratios the electric locker was available with on factory-equipped 3rd Generation 4Runners.  My 4Runner came with 4.10 gears from the factory, but I figured I might as well re-gear for larger tires while I was doing this so I went with the 4.56 3rd member (Toyota Part #41110-3D010).  Iíve provided part numbers for the other two ratios at the bottom of the page.  Keep in mind, if you choose a different gear ratio than stock, you will have to re-gear the front differential also.  Then, I figured I might as well throw in some type of traction aiding device in the front while I was having that re-geared as well.  One thing led to another, and now I have a factory electric locker in the rear, 4.56 gears, and a Detroit TrueTrac in front.  Here are some pictures of the electric locker 3rd member.  Ain't it pretty?

  Mike and I started the diff. modifications by draining the gear oil from the differential.  We then jacked up the vehicle from the frame (so the axle can hang down), and proceeded to disconnect the driveshaft.  After that, we disconnected the swaybar, lower shock mounts, upper control arms, lower control arms, panhard bar, ABS sensors, emergency brake, and brake lines.  Somewhere in the process, the suspension coils should fall out on their own.  Looking back in retrospect, it would have been a lot easier to remove the axle half-shafts first, since it would have given us more room to work, as well as made the axle lighter.  Here are a couple of pictures with everything removed.

  Once the axle was removed from the vehicle, we unbolted and removed the stock 3rd member.

Don't mind the missing stud on left, that was replaced.

  Mike removed the three studs on the right side of the housing, two of which would be reused.  He then laid the gasket down and used it as a template for the weld spots by using a piece of soapstone to outline the two sections where welding was needed, and also the section where cutting was needed.

  After building up these sections, he ground them down flat until they were flush with the adjacent gasket surface.

  Mike then fired up his plasma cutter and cut the square clearance for the locker actuator/motor.

  At this point, we placed the e-locker 3rd into the housing to see if it would fit, it did.  He marked off the four new stud locations by lightly drilling the unoccupied holes.  The next step was to drill and tap the four new stud holes.  This was probably the most time consuming part of the installation.  The hard part was trying to get the housing level on the drill press.  We ended up building a wooden box to support the housing evenly on the press platform.  Even then, we had to use little wooden shims to get it level.  The bit/tap size used was M8x1.25.  Four tapped holes later, Mike threaded the studs into the housing.  Here is the finished housing.

Notice two holes are no longer used.

  We spent a good half hour cleaning the housing of metal shavings.  We used brake cleaner and a magnet to get all the shavings and particles out.  There are two shrouds inside the axle that are removable for easier cleaning.  They prevent all the gear oil from splashing away from the differential at high speeds, so remember to put them back in if you remove them.  After we were done cleaning, Mike laid a bead of gasket sealant around the housing, placed the gasket on, and bolted in the e-locker 3rd.  We then proceeded to put everything back together (donít forget to put gear oil back in).  Plug in the differential harness, and test it out!



  Parts List

Electric locking 3rd member:
  - 4.56 ratio -> #41110-3D010
  - 4.30 ratio -> #41110-3D080
  - 4.10 ratio -> #41110-3D030

New locker diff. gasket #42181-60050

Longer diff. studs 111mm (2 required) #90116-08330

Diff. Lock ECU #89533-35070

Diff. Wiring Harness #82127-35100

RR DIFF LOCK switch #84725-35010

Radio Shack 6-Conductor Female Plug #274-236

Radio Shack 6-Conductor Male Plug #274-226

10' 18AWG/6-Conductor wire (available @ HD)



  To those of you who have always wanted the Toyota rear electric locker, but for some reason or other donít have one, Iíve provided a very easy way to retrofit one into your 3rd generation 4Runner.  If you maintain stock gear ratios, a retrofit electric locker becomes a much more cost-effective way to lock your rear than the ARB air locker Ė and no leaking air lines or compressor to worry about.

  This retrofit was done on my 2000 Toyota 4Runner SR5, V6, 4WD, ABS, Auto.  Iíve heard that those with manual transmissions have different wiring harnesses altogether, so the wiring method Iíve outlined might not apply to you.  Before you start ordering parts, check to see if you are partially pre-wired like I was.  Keep in mind that the wiring method I chose was not the cheapest (custom wiring done with relays can be done for at least $100 cheaper), but for my application, it was the easiest and provided for a very clean installation.