Toyota Tech: 'Lectric Locker
Installing an Electric Locker in a Toyota Short Cuts
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Article by Karl Bellve, photos by Ken Flesher - 4/2000

Installing the Locker into the Axle

 Selecting a Part Time Locker

There are many options for putting a traction adding device into a Toyota differential. I wanted to have a part time locker that I could deactivate when it wasn't needed due to the amount of snow and ice my truck sees during the winter. There are only two part time lockers available for the Toyota differential. The most popular choice is installing an ARB locker. This is an air-activated locker that has proven to be reliable. Another choice is the Toyota electric locking differential. Like the ARB, it acts as a spool when activated; there is no differential action and both wheels are forced to rotate at the same speed.

The Toyota electric locker uses electricity to switch from an open state to a locked state. It doesn't need electricity to maintain a state, only to switch states. An ARB requires constant air pressure to maintain a locked state. This isn't a big difference but it does mean that the Toyota locking diff will remain locked, even if the wires are torn. In an emergency, you can also remove the electric motor and manually switch the state of the locker, unlike an ARB.

One advantage the ARB has over the Toyota locking differential is speed. The ARB will activate and deactivate much faster, as long as the seals are good. The only potential problem with ARBs are the seals, which can fail, causing air leaks and differential fluid to enter the air lines or go past seals. This is rare as far as I can tell and may be due to installer error. The only problem with the Toyota electric locker, besides being slow to switch states, is that the electric motor appears vulnerable to damage. I have used this locker for most of the wheeling season without any damage to the electric motor.

So you ask, how do you install an electric locker? Read on...

 Planning and Ordering

Toyota's electric locking differential: an all-new housing, locker, gears, and bearings, all set up, with a warranty.

I first started by talking to Jay Marks Toyota about part numbers and prices. I soon bought a 1997 4Runner  electric locking differential with 4.10 gears from them. This is a V6 differential with 4 spider gears, but you can get up to a 4.56 ratio. Other ratios maybe available outside the USA but I can't find those part numbers.

The differential included bearings, housing, and the locker, shipped already setup. However, your axle housing has to be modified to fit the differential. It requires some grinding, tapping and a small touch of welding -- all simpler than setting up gears for a differential. Then, it has to be wired which is covered later in this article. The locker I bought was meant for an 8.0" Toyota axle. Erik Bibelheimer recently posted in the 4x4wire BBS that the Tacoma TRD electric locker also uses an 8.0" ring gear and what appears to be the same electric locker as Toyota used in the 4Runner. It doesn't look like this electric locker will retrofit it into the 8.4" non-TRD Tacoma axle with an open differential unless you obtain the entire TRD axle along with the locker.

The axle housing does require added clearance.

 Axle Housing Modifications

There are several things you must do to your original axle housings in order to install the electric locking differential third member. Warning: Once you have made these modifications, it might be hard to reverse them. Use the electric locking differential gasket (Toyota part 42181-60050) as a template to identify where to grind, drill and tap. The picture shows where the modifications are needed. The circles show where 4 new stud holes must be drilled and tapped. This is where the welding comes in. One of the new stud holes resides on a shoulder. This shoulder needs to be flat to make it easier to drill. If you have a drill press, you might not need to do this and may be able to avoid welding. If you do weld, you might want to widen the area that is available for the gasket surface. You have to be very careful to not overheat the housing because you can warp the ring. I also suggest that you drill and tap after you weld, just in case the welding distorts the ring a slight amount.

Compare an open differential axle housing to the electric locking differential axle housing.

The very large circle shows the area of the housing that needs to be moved backwards. One of the bolts on the differential comes into close contact in that area. A brass punch should do the trick. The rectanglar areas show the areas from which metal must be removed. Using the gasket that is meant for the electric locking differtial, mark the exact location of the stud holes and what metal to grind, then drill/grind away. You can compare the two housings here in the adjacent photo. CLICK HERE to see many more detailed photos.

Special Thanks

Few projects succeed without help from others. Special thanks to Ken Flesher for his driveway, camera, and help. Thanks also to Scott Muir for making the modifications to the housing and sending it to me. Finally, thanks to Jay Marks Toyota for a great deal on the locker.

I believe that modifying the housing is far simplier than installing a new set of gears. The beauty of this swap is that the gears are already set up! Other then modifying the housing, you just install it like any other differential third member -- just bolt it on up. The new differential uses 11 studs instead of the 10 studs used in the original differential. Two of the new studs need to be very long, over 4 inches. To make these, purchase M8-1.25 metric ready-rod, measure it, then cut it to length. The dealer also sells these 111mm studs for a few dollars, as part 90116-08330.

You might want to do some preventative maintenance while you have the axle shafts out. There are two internal seals that about $4 each and two O-rings for the same amount. You can also replace the axle bearings but they need to be pressed out with a SST.

Wiring the Electric Locker


Wiring the locker was more difficult than actually installing the locker. The easiest solution is to buy the locker ECU from Toyota. This part costs over $100. If you are not comfortable with soldering, wiring, or electricity, I would suggest buying the factory ECU. You might also find one in a salvage yard in a late-model 4Runner or a FZJ80 with factory electric lockers.

With the help of Scott Muir, I used an inexpensive dual relay system that he built and designed to control the locker. It basically works like a solenoid control box for a winch, using the following parts:

You can get the relays, resistors, and a box from an electronics store like Radio Shack. The 6-conductor wire is a little more difficult to locate; don't bother looking for it at the local hitch shop. I only found it at a major RV shop. You'll have to get the Toyota harness from the dealer or a salvage yard. Also think about how you want to bring the wires into and out of the relay box. On my relay box, we used connectors on either side of the box to allow us to disconnect the box from the wiring. CLICK HERE to see many more detailed photos.

 Analyzing the Wiring

The differential has several bundles of wires coming out of it in two separate connectors, one is a 6-pin connector and the other is a 2-pin connector. Two wires from the large 6-pin connector carry the power to the electric motor on the differential. These wires drive the electric motor in forward or reverse to lock or unlock the differential. These wires will be colored Green (G) and Green with a Red (G-R) stripe.

Three other important wires come from the same large 6-pin connector on the differential. These wires are attached to something called a limit switch inside the differential. The limit switch indictes the position of the locker. This switch controls a relay box that cuts power to the motor once the locker has fully transitioned from one state to another. Among these wires is a White wire with a Black (W-B) strip; it brings ground to the switch. The other two wires, Green with a Yellow (G-Y) stripe and Green with a Black (G-B) stripe, bring ground out of the switch, depending upon the state of the locker.

8-pin Connector Wiring
# Color Purpose
1 Blue-Yellow Lock Sensor
2 Green-Yellow Limit Switch-Unlocked
(used to lock)
3 Green-Black Limit Switch-Locked
(used to unlock)
4 White-Black Limit Switch-GND
5 Not Connected  
6 Green Motor Power
7 Green-Black Motor Power
8 White-Black Lock Sensor Ground

For example, if the locker is locked, then the G-B wire is grounded has continuity with the W-B wire. The G-Y wire is not grounded in this situation. In this state, the G-B wire indicates that the locker is not in an unlocked state. As soon as the differential completely unlocks, ground interrupts to the G-B wire, and switches to ground the G-Y wire. This can be confusing, but the key concept is that the G-Y and G-B wires, cut power or give power to the electric motor through the relays.

The two wires that come out of the differential and terminate in the 2-pin connector attach to a sensor that indicates if the locker is actually locked. I use this to power a light on my dash. One of these wires is Black with a White (B-W) stripe and the other is Blue a Yellow (BL-Y) stripe. When you wire everything up, you will notice that there are two B-W wires, one coming from each connector. I joined these two wires into one ground wire.

If you buy the factory wiring harness that connects between the frame harness and the differential's two connectors, it only has one 8-pin connector. The sidebar table shows what the wires do on that 8-pin connector.

 My Installation

Let me describe how I put everything together. I cut off the 8-pin connector from the end of the factory wire harness and and soldered on a female 6-pin connector that I got from a RV center. On the male side of the connector, I soldered the 6-conductor RV wire. I then wound this up through a rubber grommet in the body to the pillar by the passenger side door.

There 4Runner electric lockers have several differences, depending upon the year of the vehicle. My locker only had one spring in the gear assembly while other years of the locker have two. With only one spring, the motor wouldn't slow down fast enough when the power was cut, so it would jam. If your electric motor is jamming, you may want to put resistors inline with the motor. I use two 10-ohm, 20-watt resistors in parallel with one of the motor wires to slow the motor down, curing this problem. The two 10-ohm resistors, used in parallel, provide 5 ohms of resistance and can handle 40 watts of power, which is plenty for this motor.

I then soldered another 6-pin connector to connect the harness to the relay box. I mounted the relay box to the pillar with velcro tape, and used a wire to ground the relay box to the truck body. CLICK HERE to see many more detailed photos.

Wiring Schematic Using Relays

Erik Bibelheimer and I worked up the attached wiring diagram, to help clarify everything.

 An Alternate Installation

Here is an alternate way to wire the locker just using a DPTP switch.

Wiring Schematic Using DPTP Switch

This method does mean that the Locking Position Switch needs to act as the ground for the electric motor. I am not sure it is up to the task but Carl Whitmore is using it this way and reports no problems.

Part Number Quantity Description Source
41110-3D030 1 4.10 Electric Locking Differential Toyota
42181-60050 1 Gasket for Electric Locking Differential Toyota
90116-08330 2 111mm Studs Toyota
82127-35100 1 Wiring harness from Differential Toyota
  2 10A 12V relays and bases Radio Shack
  1 1 inline fuse with 10A fuse Radio Shack
  2 12V LEDs (red and green) Radio Shack
  1 15' 14 gauge 6-conductor wire RV store

Contacts Related Links
Jay Marks Toyota
Dept OutdoorWire
11711 Gulf Freeway
Houston TX 77034 U.S.A.
Phone: 713-943-7010
Fax: 713-943-8930

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