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Originally Posted by tacosupreme
All of the wires from the aforementioned locations all end up in one place, Connector F-13 on the 4wd ecu. Pin 15 goes from +12VDC to -12VDC as soon as low range is selected, same with pin 17, pin 13, pins 23 and 24. Seeing a theme? How much of a "rat's nest" would it be to tap into those wires with a grounded switch? Or, at least in my case, find out where those ground signals feed into on the circuit card and solder on a jumper there. If I get it to work I could even order a female and male connector and just make a "plug and play" mod to make it easy for everyone.
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All I'm saying is the 04 and earlier tacomas has a
separate unit for
4WD control and for the
Rear-Differential lock control.
2 Computers! Except for ONE wire, they are completely isolated from each other. That is the one wire you ground in the "grey wire mod". You are ONLY tricking the rear differential computer into thinking it is in 4LO. The actual 4WD computer still reads the correct sensor readings to deterimine what gear it is in for proper shifting & engagement. That is how it works on an '04 or earlier. (keep that in mind when trying to trick the '05 computer that conrlos BOTH with only ONE signal.)
An '05 Prerunner computer works almost exactly the same as the '04 rear differential computer, only it has no 4WD control portion (neither built in, nor an external computer). That's why it engages in 2HI.
The '05 4X4 computer we have been talking about has both computers integrated into ONE. There is NOT a separate control unit. That is the problem. You need to send a ground signal to the Rear differential lock portion of the computer
ONLY, but you still need the SAME signal for the 4WD control. And there are several different sensors that provide feedback to the computer to do so. That is why
you cannot simply ground a wire or fake a signal to the 4WD ECU to get the rear differential lock to work. You will have to try and fake ONLY the rear differential lock portion of the
circuit board, but NOT the 4WD control portion of the
circuit board. (but they both read from the same signal). That's an internal computer wiring issue. Forget trying to trick the computer with a false signal with the external wiring. The 4WD potion of the computer still needs that signal.
What signals does the 4WD computer need to shift properly? You need pin numbers? Ok, how about
ALL of them except for pins 1, 2, 13, 16, 20, & 21 of plug F12(A). Those are for the differential lock. The 4WD needs the signals from all the other wires to work properly. Your problem with the little test you did was that pin 16 (plug F12) from the OEM switch was still engaged when you disconnected everything.
Make sense? Basically In order to do all THAT, without adding other components (another computer or independent actuator control), you would have to map the circuit board, isolate the rear differential control from the 4WD control, and ground the proper circuit (rear-diff) after you isolate it from the 4WD. Not an easy endeavor, but maybe as a chip repair guy you can handle it. (just follow pin 17 yel/blk wire on plug F13(B) to the circuit board & see where it goes) This is not a try, try again job though. Once you screw up the circuit board your f'd! (tacosupreme may be able to repair his... that's what he does. Your typical DIY'r cannot)
Engaging the lock and then tricking all the sensors to make it think it is unlocked and them switching out of 4LO, actually isn't that bad of an idea. You just have to do a little more than expected. (If you don't cut the ground to the wire in the right spot, the ABS might re-engage as well, since your pulling that signal from the computer to make it think it's unlocked).
Here's what you need:
At the flip of a switch, you need to disengage:
-The (rear diff) indicator switch
-The limit switch wire for the engaged posistion,
-But Re-Engage the limit switch for the "disengaged" position
-Also need to disengage the power lead from the OEM locker switch to the 4WD computer
-If you do all that, you MIGHT be able to leave the actuator alone, but since your doing all that, I would also disengage that, just in case.
You need all this to be done SIMULTANEOUSLY so the computer doesn't go haywire and/or the locker doesn't try to disengage. IF this works successfully, you may still have to switch BACK to 4LO in order to disengage it. Not positive, but it's possible if you have it in 2HI or 4HI and the computer suddently senses the locker is engaged, then it might go haywire again.
Test it again, except this time, remove the key from the ignition... disconnect the wires
and disengage the locker switch. (this just simulates EVERYTHING being disconnected simultaneously until the power is turned back on). Then turn it back on and switch to 2HI or 4HI. If it works, turn off the ignition (leave it in 2HI or 4HI), plug in all the wires and re-engage the locker switch, and see if it causes some trouble (Which will verify the validity of my re-enagement theory... if it really has to be done in 4LO).
If it all works, I can work up a basic wiring diagram later just to show you what all is involved in the rewiring. You'll possibly need a switch with the ability to interupt power on 3 different lines (6-pole) and probably one relay (at the LEAST). If that switch is not available you may need as many as 4 relays. (that's where that "rats nest" comes in)
Try it and tell me what you think!