Toyota made the differential lock feature available in 4Lo only on TRD 4WD Tacomas. Several theories have been tossed around as to why Toyota did this, but the most sensible is that they are covering themselves legally, as driving at higher speeds with a locked rear differential can be an interesting experience. One odd thing, however, is that on Pre Runner Tacomas, the locker is available at all speeds since there is no transfer case to dictate when the locker can be activated.

We all know how helpful a locking differential is off hwy. Using the locker in 4Hi as well as 4Lo is desirable. Two methods have been devised to defeat this 4lo only locker option. The first was a modification to the blue plug that is connected to the transfer case/transmission combo. The problem with modifying the locker using this Blue Plug Mod was that it made the main ECU think the vehicle was in 4lo all the time, thus effecting shift points on automatic transmissions. This was an undesirable side effect.

The second and preferred method is known as the Gray Wire Locker Mod. The 4WD computer is tied to the main ECU. A gray wire is shared between these two computers. When the vehicle is placed in 4Lo a ground signal is sent down this gray wire to the 4WD computer. This ground signal allows the locker to be activated should the button be depressed. The ground signal also goes to the main ECU telling it the truck is in 4Lo and thus changing the shift points. By sending a ground signal ONLY to the 4WD computer, the locker may be activated in 2Hi, 4Hi, or 4Lo, yet the main ECU is not effected so the shift points will only change if the truck is actually in 4Lo.

TOOLS REQUIRED:

To complete this mod youíll only need some wire cutters, a 12 piece of wire, a butt connector, a ring connector, some electrical tape and a philips head screw driver. If you want to match the wire in the truck, you'll need 18ga. I had 14ga on hand so that's what I used and it worked fine.

The 4WD computer is located behind the driverís side kick panel. To get to it, just remove the four screws in the door trim, and pop it out the trim out. The kick panel will then slide out.

DRIVER'S SIDE KICK PANEL                                 REMOVE DOOR TRIM SCREWS

 

The 4WD computer is toward the back of the panel area close to the firewall. It's obvious which box is the 4WD computer by the decal placed on it.

4WD COMPUTER LOCATION                                         4WD COMPUTER LABEL

 

Simply unplug the white connector going into the 4WD computer and remove the tape and protective sheathing.

UNPLUG THE WHITE CONNECTOR
 

Make a 12 patch wire. If you want to match the size of the gray wire then use 18ga wire for the patch. I used 14ga since that's what I had on hand, and it worked fine. Crimp a butt connector on one end of the patch wire, and a 3/8 ring connector on the other end. Once you're sure both the ring and butt connector are secure, cut the gray wire about 3 from the white 4WD computer connector and splice the patch wire to the gray wire. Make sure you splice into the end coming from the white connector.

Note: In some rare cases, there is a different color wire used in place of the grey wire. The best way to identify the correct wire is to locate prong number 8. This wire is in the bottom middle of the plug, between a green/yellow wire and a white/black wire. See this wiring diagram for more info.

 

                12 PATCH WIRE                                          SPLICE PATCH WIRE INTO GRAY WIRE
  

 

Next, locate a screw to ground to. Any screw going into the body will work. The one I used is right above the 4WD computer and already had some equipment grounded to it. Itís a 10mm brass colored bolt which is easy to reach and is an excellent candidate. I taped up all connections for added protection against shorts, as well as to keep the wire from pulling out of the connectors. I also recommend putting a small piece of electrical tape over the unused end of the gray wire for protection against a short. The unused end will be the end running up into the dash.

10mm BRASS COLORED GROUND SCREW                   TAPE OFF UNUSED END OF GRAY WIRE

 

 

That's all there is to it. Total time to complete this mod should be less than 30 minutes. As you can see from the following pictures, the locker will activate in 2Hi, 4Hi, and 4Lo. My 99 TRD is equipped with ABS, so anytime the locker is activated, the ABS is disabled. This is denoted by the ABS light being illuminated. This is how it worked from the factory, only before this mod ABS was only disabled in 4Lo when the locker was activated. Now I can have the locker activated while in 4Hi and at the same time the ABS will be disabled. You can't beat that.

  LOCKED IN 2WD ABS DISABLED                             CLOSE UP OF LAMPS FOR CLARITY

 

 

LOCKED IN 4WD HI ABS DISABLED                          CLOSE UP OF LAMP FOR CLARITY