It works!
I've modified the wiring to the Diff Lock Control Unit - now my rear e-locker will lock up in 2WD, 4HI and 4LO. I used a DPDT relay and a lit rocker switch controlling the relay to switch both power and ground.
When I flip my rocker switch in 2WD, 4HI or 4LO, I get a lit DIFF LOCK light on the instrument cluster, and nothing else. So, I can have a locked rear diff and keep ABLS to the front wheels.
I verified the diff is actually locked by putting the truck up on jackstands, locking the rear diff in 2WD, shifting to Neutral and spinning one rear tire - the other tire spins the same direction. (An open differential would cause the tire to spin the opposite direction.)
I also verified the diff is actually locked by playing in the dirt. In 2WD with the diff locked, I lay down two beautiful marks with no SLIP light. While turning, the inside rear tire slips - it's obvious the diff is locked.
I'm still able to lock the rear diff in 4LO using the OEM switch.
I used a separate rocker switch (instead of using the OEM switch) and a DPDT relay so that the installation wouldn't cause any malfunction lamps, blinking no-worky lamps, or other unintended results.
First - a failed attempt:
I tried to simulate the transfer case in 4LO by grounding out the 4LO switch. Here's a bit of info about that:
The 4LO switch is a normally open switch, and it closes when the transfer gear is under 4LO condition, detected by the L-H shift fork position. The 4LO switch is located on the transfer case, just inside of the front prop shaft flange. The 4LO switch inputs to the Transfer Control Unit.
I jumped across the 4LO switch, and across the 4LO and the Wait Detection Switch. All it'll do is confuse the Transfer Control Unit. The problem is that the 4WD Shift Switch inputs to the Transfer Control Unit, which then compares it to the various sensors on the transfer case.
With the 4WD Shift Switch in 2WD or 4HI, when you jump the 4LO switch (pin 24 to ground) you'll get a flashing 4LO light - indicating a faulty 4LO switch or faulty wiring to the 4LO Switch.
With the 4WD Shift Switch in 2WD, when you jump the 4LO switch (pin 24 to ground) and the Wait Detection Switch (pin 17 to ground), the 4WD Shift Indicator Lamp (the little drivetrain picture that tells you if you're 2x4 or 4x4) will go out and the 4WD Warning Lamp (the lamp that says 4WD) will flash.
The problem is that the 4WD Shift Switch inputs to the Transfer Control Unit, which then compares it to the various sensors on the transfer case. When the 4WD Shift Switch position isn't consistent with the position sensors on the t-case, you get blinking lights and no-worky.
Having failed at tricking the control units into thinking conditions are met to lock the rear diff, I bypassed the control units entirely – I wired 12volt power directly to the diff lock solenoid.
Here a picture where all the stuff is:
![Image]()
Here are a couple wiring diagrams:
![Image]()
![Image]()
Here’s a pin explanation:
![Image]()
+12volts is applied on terminal 12, with terminal 11 being switched ground – power to the diff solenoid is controlled by switching the ground at terminal 11. I’m betting the diff control unit can isolate the +12volts on terminal 12, so I wanted to switch both power and ground.
Here's how I wired it:
The quick’n’dirty:
Cut the [Y] yellow wire at terminal 12 at the diff lock control unit harness.
Cut the [V] violet wire at terminal 11 at the diff lock control unit harness.
Strip insulation from black wire at terminal 3 at the diff lock control unit harness.
Strip insulation from [R/B] royal blue wire at terminal 1 at the diff lock control unit harness.
Connect DLCU side of yellow wire to relay terminal 1.
Connect jumper from royal blue wire (power) to relay terminal 3.
Connect diff lock solenoid side of yellow wire to relay terminal 5 (diff lock solenoid terminal 4).
Connect DLCU side of violet wire to relay terminal 2.
Connect jumper from black (ground) wire to relay terminal 4.
Connect solenoid side of violet wire to relay terminal 6 (diff lock solenoid terminal 2).
Connect jumper from royal blue wire (power) to hot side of rocker switch.
Connect jumper from black wire (ground) to other side of rocker switch.
Connect jumper from load terminal on rocker switch to relay terminal 7.
Connect jumper from relay terminal 8 to black wire (ground).
![Image]()
I'll post some pics of the install in a bit.
I've modified the wiring to the Diff Lock Control Unit - now my rear e-locker will lock up in 2WD, 4HI and 4LO. I used a DPDT relay and a lit rocker switch controlling the relay to switch both power and ground.
When I flip my rocker switch in 2WD, 4HI or 4LO, I get a lit DIFF LOCK light on the instrument cluster, and nothing else. So, I can have a locked rear diff and keep ABLS to the front wheels.
I verified the diff is actually locked by putting the truck up on jackstands, locking the rear diff in 2WD, shifting to Neutral and spinning one rear tire - the other tire spins the same direction. (An open differential would cause the tire to spin the opposite direction.)
I also verified the diff is actually locked by playing in the dirt. In 2WD with the diff locked, I lay down two beautiful marks with no SLIP light. While turning, the inside rear tire slips - it's obvious the diff is locked.
I'm still able to lock the rear diff in 4LO using the OEM switch.
I used a separate rocker switch (instead of using the OEM switch) and a DPDT relay so that the installation wouldn't cause any malfunction lamps, blinking no-worky lamps, or other unintended results.
First - a failed attempt:
I tried to simulate the transfer case in 4LO by grounding out the 4LO switch. Here's a bit of info about that:
The 4LO switch is a normally open switch, and it closes when the transfer gear is under 4LO condition, detected by the L-H shift fork position. The 4LO switch is located on the transfer case, just inside of the front prop shaft flange. The 4LO switch inputs to the Transfer Control Unit.
I jumped across the 4LO switch, and across the 4LO and the Wait Detection Switch. All it'll do is confuse the Transfer Control Unit. The problem is that the 4WD Shift Switch inputs to the Transfer Control Unit, which then compares it to the various sensors on the transfer case.
With the 4WD Shift Switch in 2WD or 4HI, when you jump the 4LO switch (pin 24 to ground) you'll get a flashing 4LO light - indicating a faulty 4LO switch or faulty wiring to the 4LO Switch.
With the 4WD Shift Switch in 2WD, when you jump the 4LO switch (pin 24 to ground) and the Wait Detection Switch (pin 17 to ground), the 4WD Shift Indicator Lamp (the little drivetrain picture that tells you if you're 2x4 or 4x4) will go out and the 4WD Warning Lamp (the lamp that says 4WD) will flash.
The problem is that the 4WD Shift Switch inputs to the Transfer Control Unit, which then compares it to the various sensors on the transfer case. When the 4WD Shift Switch position isn't consistent with the position sensors on the t-case, you get blinking lights and no-worky.
Having failed at tricking the control units into thinking conditions are met to lock the rear diff, I bypassed the control units entirely – I wired 12volt power directly to the diff lock solenoid.
Here a picture where all the stuff is:
Here are a couple wiring diagrams:
Here’s a pin explanation:
+12volts is applied on terminal 12, with terminal 11 being switched ground – power to the diff solenoid is controlled by switching the ground at terminal 11. I’m betting the diff control unit can isolate the +12volts on terminal 12, so I wanted to switch both power and ground.
Here's how I wired it:
The quick’n’dirty:
Cut the [Y] yellow wire at terminal 12 at the diff lock control unit harness.
Cut the [V] violet wire at terminal 11 at the diff lock control unit harness.
Strip insulation from black wire at terminal 3 at the diff lock control unit harness.
Strip insulation from [R/B] royal blue wire at terminal 1 at the diff lock control unit harness.
Connect DLCU side of yellow wire to relay terminal 1.
Connect jumper from royal blue wire (power) to relay terminal 3.
Connect diff lock solenoid side of yellow wire to relay terminal 5 (diff lock solenoid terminal 4).
Connect DLCU side of violet wire to relay terminal 2.
Connect jumper from black (ground) wire to relay terminal 4.
Connect solenoid side of violet wire to relay terminal 6 (diff lock solenoid terminal 2).
Connect jumper from royal blue wire (power) to hot side of rocker switch.
Connect jumper from black wire (ground) to other side of rocker switch.
Connect jumper from load terminal on rocker switch to relay terminal 7.
Connect jumper from relay terminal 8 to black wire (ground).
I'll post some pics of the install in a bit.
