Custom Switch Wiring for Aftermarket Front & Rear Lockers

Goal
Install my own custom FRONT LOCKER switch and wiring that will only engage when the truck is in 4 LOW, 2 LOW is not engaged, and the ignition is ON. Also, the switch button is to only light up as ON when it is actually ON. I want to be able to use the FRONT AIR LOCKER and the stock REAR E-Locker independently on my 3rd Gen Manual Off Road Tacoma. I wanted a button operation that was intuitive like the stock rear locker button, which only works in 4 LOW.


Yellow wires and black/white ground wire locations shown at pins below:


Variations
This could be used to wire an aftermarket REAR LOCKER, a FRONT LOCKER, or both, with slight modification of the diagram below (splice off of Relay B, Terminal 30(3) to add an additional relay for another switch). You could also wire directly into the 4WD wires without the 2 LOW Plug-and-Play harness (would then omit Relay A and then run the tapped F12 Pin 4 ignition wire to both Terminals 86(1) and 87(5)).

Build Difficulty
Intermediate to Advanced. You must know how to use crimpers, shrink tubing, solder or good crimp tubes/taps, and a voltmeter to verify wire functions and to troubleshoot any problems.

Relay reference info
Alternatively to the BOSCH style relays shown above, you could use smaller Micro Relays like I did (Micro Relay terminal numbers in parenthesis below with description of each typical terminal use):
*85(2) Signal Positive 12V+; feeds from switch
*86(1) Signal Ground
-Tip 1: You can switch the two terminals above in most relays, if there isn't a diode in your relay
*30(3) Input Power Positive fused 12V+ that will power accessory
*87(5) Triggered 12V+ output to accessory when switch closed (when power supplied to terminal 85(2))
*87a(4) Power goes to this terminal when switch open (this is the at rest position when no power supplied to terminal 85(2))
-Tip 2: Alternatively, power can be supplied from 87(5) or 87a(4) to feed the accessory connected to Terminal 30(3), for this low amperage use.
-Tip 3: Relays are described with two Amp ratings, the smaller being the Amperage limit for power between Terminals 30(3) and 87a(4), the NO (normally open) position. The bigger Amperage rating is for power between Terminals 30(3) and 87(5). the NC (normally closed) position, which is usually what you power your accessory through.



Limitation & Liability Disclaimer
This thread is dedicated to the locker switch's wiring to the 4WD system. I'm sure there are plenty of other thread resources to address compressors, overhead button wiring, fused power sources, and ARB's off-the-shelf locker wiring systems, but if there isn't, I'd be happy to chime into those threads separately.

This post is only regarding the wiring for the front locker switch on my 2019 Tacoma Off Road Manual Transmission, your truck may vary, please verify your specific vehicle specs. I am not a mechanic or an electrician, but rather an engineer of another study, that has an interest in the end goal, and am working my way through this great resource to get there. Hopefully you can use this as a reference if this is something you’d be interested in doing. I'm not going to spend a lot of time responding to "why do I need this?" responses. If you have a need and the ability, feel free to use this. This is for information only and I am not responsible for any modifications you make to your vehicle, or any resulting damage or injury. @BigWhiteTRD came up with the final design, and I am posting this because I did the installation and testing. He’s not responsible for your shenanigans either. This is an open, public, shared design that anyone is free to wire on their own or mass produce (@BigWhiteTRD says it would be really nice if you hook him up with a sample, if you’re going to be selling a product from his design).

Partial Shopping List
I bought a CH4x4 small button ON-OFF switch for my overhead switch panel to operate an ARB front air locker.
https://www.ch4x4.com/product/ch4x4-small-push-switch-for-toyota-front-locker-symbol/


Here’s the diode I used. Apparently getting a Schottky type 15amp is important:

$6 MCIGICM 20Pcs 15SQ045 Schottky,15amp Diode Axial Schottky Blocking Diodes

https://www.amazon.com/gp/aw/d/B07NS63XJH?ref=ppx_pop_mob_b_asin_title



I believe 18 gauge stranded copper wire should be sufficient for all of this (don't get silicone coated wire, it's too flexible). The actual load to the ARB Front Locker Solenoid is only 1A. I ran 18 AWG between the relays and then 14 AWG all the way to my ARB locker solenoid in my truck bed. I was able to buy some bundled 14G wires (3 way, with 3 in the same jacket, and some 2 way) from Amazon and ACE Hardware, which simplified running wires to my switches, solenoid, compressor, and other accessories I wired up.

$22 Geosiry 14 Gauge Wire, 30FT Flexible Stranded Tinned Coppe Cable, Low Voltage 12V Wire for Automotive, Marine, Home Improvement, and DIY Projects (14 Gauge, 30FT)

Geosiry Electrical Wire - 30Ft 14AWG Tinned Copper Hookup Wire, UL2464 2 Core Flexible Extension Power Cord for Auto，Insulated Stranded Cable for Lighting Boat Marine Solar -Black (14AWG 30Ft): Amazon.com: Tools & Home Improvement

You’ll need some big and medium female spade terminals if you use the micro relay below. Otherwise just big spade terminals for a typical BOSCH style relay. Get some with, or add some, adhesive shrink tubing, to keep the wires from pulling out and to isolate the terminals. These are really nice for big terminals, but I cut the shrink tubing down a little on the ends before putting on the terminals, but if you waited to shring it after it was on the relay, it could help glue it on:

$25 Haisstronica 260PCS Heat Shrink Spade Connectors - Quick Disconnect Female & Male Spade Terminals for Watercraft, Electronics & Automotive

haisstronica 260PCS Heat Shrink Spade Connectors-Electrical Spade Wire Connectors-Quick Disconnect Connectors -Female and Male Spade terminlas for Watercraft,Electronics,Automotive Crimp Connectors: Amazon.com: Industrial & Scientific


Micro Relays: I used Hella 5 pin Micro Relays from Orielly’s that ended up only costing about $3 a piece:
Import Direct Ignition 30 Amp 5 Terminal Relay Part # 250594 (it is a HELLA product in the box, I don't know the HELLA part number offhand)
https://www.oreillyauto.com/detail/...otive-car-1950-mercury-mercury?q=250594&pos=0

And for good measure, I've found this electrical tape to be the best I've ever used. It is stretchy and sticks to itself really good. I'm on my second box of it.

$19 Lichamp 10-Pack Black Electrical Tape Waterproof, 3/4 in x 66ft, Industrial Grade UL/CSA Listed High Temp Electrical Tape Electric Super Vinyl

https://www.amazon.com/dp/B07VNTC9LH?ref=ppx_yo2_dt_b_product_details

Background and my build
I already have a VIAIR onboard compressor and air tank on the bed, so I didn’t want to use ARB’s wiring. I also already installed @lapoltba plug and play 2 LOW switch. I was afraid that if using the ARB wiring, I could cause an accidental actuation of the front locker if the button was accidently pushed (ARB is set up so that when the compressor is on, the front locker can be engaged, or if you have their rear locker, then when the compressor is on and the rear locker is engaged), which may possibly be problematic if I was in 2 LOW (maybe one front wheel would start getting power), or 4 HI. My air tank is always charged, and I often have the compressor on to keep it charged, so the ARB stock wiring setup wouldn’t work for me. This is all speculation, but I just wanted to be careful. I also read examples of when only engaging the Front Locker would be good, so I couldn't just run a single relay off the rear locker wiring for this.

I figured there would be a way to tap into that 2 LOW plug-and-play harness to meet this goal, so that I didn’t have to tap into any important stock wiring directly. It would also make installing the wiring super easy if the whole setup was now Plug-and-Play after wiring it up on the bench.

I wracked my brain and couldn’t come up with something good, so I reached out to the original creator of the wiring diagram for the 2 LOW for advice @BigWhiteTRD. With some back and forth, he came up with some good designs, and with some troubleshooting, came up with the latest one above.

Link to 2 LOW threads by @BigWhiteTRD and @lapoltba that show the wiring schematics pretty well and how to access the 4WD wires, and installation of the Plug-and-Play harness:

https://www.tacomaworld.com/threads/lock-stock-and-2wheel-low-3rd-gen-diy-mod.536677/

https://www.tacomaworld.com/threads...-2wd-low-range-for-the-3rd-gen-tacoma.614743/

Build in progress pictures





Splicing diode into F13 Pin 3 in the 2 LOW plug and play harness. This is a ground signal, and the key to the whole setup. This is so it knows when you are in 4 LOW (we are supplying an ignition 12v+ current through the relay to F13 Pin 3, which is a switched ground, meaning if the truck is in 4 LOW, the current passes through, but if not in 4 LOW, the truck turns off the ground path). If you were to splice into the truck wiring directly without this plug and play harness, it’s the yellow wire in the big plug (see plug in first images or again further below).


Splicing into the two signal wires of the 2 LOW Plug-and-Play giant relay, which is used as a safety to prevent the Front Locker from engaging when in 2 LOW. This isn’t needed if you don’t have a 2 LOW switch. I added additional splices of the ground wire downstream (my brown wire is the ground). Verify with a voltmeter which one is the ground while plugged into the truck (or follow the wires to the connector terminal), since these terminal wires could be reversed and still work. Alternatively, you could provide a separate ground source and just tap the hot side, but then that's more wiring to do after installing the plug-and-play 2 LOW harness


Not shown is the tap into the F12 Pin 4 of the Plug-and-Play harness, which is a 12V+ ignition power source (only on when ignition on). Here's the plug image again for reference.


All done. FRONT LOCKER button pushed ON and not illuminated and not ON because not in 4 LOW, or ignition not on, or 2 LOW is also pressed.


All done. FRONT LOCKER button pushed ON, while in 4 LOW (ignition is on, and 2 LOW button not pressed), so now lights up and FRONT LOCKER ENGAGED.

WARNING
The first iteration of this allowed a direct current from the diode back to the switch. The diode had just enough backfeed that the switch was lit up ever so slightly whenever the ignition was on (diode wire came out of CH4x4 wire 4 ground, and wire 3 was dash light, but it lit up like there was a current through wires 1 to 2). We changed the path and isolated the switch, and added the bonus that it would only light up when actually on. So keep this in mind if you’re trying to come up with simpler alternatives.

Also, I provided a separate constant fused power source to directly power the ARB Front Locker Solenoid (from Terminal 30(3) on Relay C). I wanted to minimize any additional load or failure points that could be introduced to the 4WD system. If I ran the tapped ignition wire (if I skipped the last relay and fed the Locker switch output directly to the ARB solenoid), and somewhere along that extra 20’ of wire got pinched or cut, it could short my 4WD system.

Thanks
This is my first post, so please excuse my formatting as I learn this site. I hope this helps someone. I imagine a more common use would be for people adding rear lockers to the Sports. Good luck. I just got my front locker and regear installed, and so far, so good. This website has provided me with so many mod ideas, and I've done a lot of the electrical mods I could find in here for a 3rd Gen, as well as a lot of custom additions and improvements. The wiring diagrams, pictures, videos, and discussions on here have made them so much easier to build, so this is my attempt to make a contribution back. You've helped give me something "productive" to do in these last 2+ years of COVID isolation, so I can come out charging. Thanks everyone!

 

Reserved for possible additions/variations

 

Standing by to answer anything I can.

Thanks again for @CAtacoWaves for the extensive write-up. It can seem like it takes longer than doing the mod to write it up

 

Haha, only crickets remain.

 

Yeah
I can have that effect

 

Why on earth is it part of your goal, for your locker to be limited to 4Lo only (same as stock rear locker)? I consider it a MAJOR drawback of the truck, not being able to engage my locker whenever I feel like I need it... It would help get through some obstacles in 2wd, without even needing to engage 4wd at all. And, if I could, I would probably be using my locker in 4hi all the time!

 

Interesting. I was just thinking “in the box”. Could you provide context and examples for when you would use a locker outside of 4 Low? Do you have experience with this in older models or custom setups? I have not yet hypothesized a situation that I wouldn’t want to have both the advantage a locker and low gearing at the same time, so I’m interested to hear. That would obviously allow for much simplification, or make this mod irrelevant.

In my installation, I have a stock e-locker in rear and used this to add a front air locker. I can run either locker independently, but always in 4 Low. I also drive a manual transmission, so clutch burn is a thing if I’m trying to get unstuck or crawling in Hi gears.