2019+ Tundra Alternator Charge Voltage ALT-S Circuit Existence?

I did an extensive amount of searching and didn't really find any conclusive evidence other than anecdotal stories of failed attempts at alternator charge voltage adjustment on the 2019+ 3rd gen Tundras.

Has anyone with a 2019+ Tundra successfully been able to adjust the charge voltage of your truck for AGM batteries by manipulating the ALT-S circuit?

I found the HKB Electronics micro fuse https://www.hkbelect.com/product/438-mk2-micro-blade-5a-electronic-fuse-version-2019/ and the site states that it will only work if the 2019-2020 trucks have an ALT-S fuse. I popped the fuse box in my truck and low and behold, the ALT-S fuse spot was there along with a 5A fuse populating the slot.

I know on the Tacoma's, they completely lack the ALT-S fuse/circuit so I'm wondering if the ALT-S fuse is just a redundancy from the pre-2019 Tundra fuse boxes (i.e. why change the fuse box), and while I can sink $50+ a couple of weeks of waiting, I figured I'd ask to see if anyone has been successful here already.

 

I have a ARCLight LEDs adjustable voltage booster sitting in my pile of stuff to go in with the dual AGM's/etc on my 2021; however, haven't looked for the ALT-S fuse, I just hoped for the best... My '18 4Runner has the ALT-S fuse, and subsequently have used both the GM Diode and the ARCLight adjustable unit on that truck, but I know the 2020+ 4Runners got rid of it (and completely changed the fuse box).

If no one else answers, I'll be picking my truck up from it's first transformation (lift, wheels/tires, snorkel, etc) on Thursday and will check then

 

Yes, many people have used the HKB booster fuse to bump up their voltage, just do a search for HKB there are a few threads

 

Specifically on 2019+ Tundras? The posts that I found all referred to pre-2019 Tundras.

 

OK. Just as an update to this thread, I got my Genesis Off Road Dual Battery setup installed with two Fullriver Full Throttle batteries. I ordered 2 MK2 HKBs (one spare) around the time I made this thread, but of course they are still in the mail and will probably show up in the second half of this year.

In the mean time, I got my hands on a GM diode and followed the guide here: https://www.chitown4x4.com/agm-battery-voltage-upgrade.html

In my fuse box, the GM diode "arrow" pointed towards the front of the truck in the ALT-S slot. The diode successfully boosted the charge voltage by ~0.5 V in my truck, and when my MK2 HKB shows up I will be swapping the GM diode out for the MK2, just to have a little more reassurance/actual fusing.

All in all, I can confirm that at least on my 2019, ALT-S circuit modification is still an effective way to bump alternator charge voltage.

 

Sorry for the late reply, I can confirm my 2021 still has the ALT-S fuse as well, hoping to be at the point of reconnecting the battery later this afternoon and will verify the voltage increase

 

Curious how it goes. I have an Arclight Voltage Booster from my 4Runner as well that I'd like to try.

 

I have a 2019 and use the HKB.

 

I still have an HKB fuse for sale if anyone is interested..
I no longer use an AGM battery and have no use for it..

HKB Electronics Alternator Voltage Booster - MK2 Micro blade 5A | Toyota Tundra Forum (tundras.com)

 

So, on my 2020, the Alt-S fuse is the 5A and the Arclights are intended for the 4Runner's Alt-S with the 7.5A. Seems like it would be okay to put the 5A in there? (electrical is clearly not my strong-suit)

 

Not to bump a month+ old thread, but I just installed the HKB MK2 on my Tundra (I received it a few weeks ago but didn't get around to installing it until now) and the charge voltage is still bumped, so either solution (HKB) or GM diode will work.

 

Can confirm, GM diode works on my '21... I have the Arc Light LEDs adjustable booster, however, both modes decreased voltage. Looking back, I'm assuming this means that it could have been installed backwards, but the clearance doesn't really exist for it to sit well in the other direction.

With the GM diode I'm >14.2v almost always, and up to around 14.5-14.6 at cold start

 

Interesting, was your battery light on the dash?

 

Yep. Turning it to "bypass" or inserting the gm diode solved the battery light and increased the voltage... I sent an email to him over the weekend to see if he had any input; I understand it isn't marketed for these trucks

 

Did you ever hear back from arc light? I ran into the same issue as you with it not fitting in the right orientation.

 

Nope never got a response and never pushed contacting them further

 

You put the GM Part no. 12135037 diode in for the alt fuse? Just trying to confirm before I order this and the X2 27F for my 2021.

 

Yes that GM diode works in my 2021, almost 2 years now. The parasitic drain is high on our Tundras, agm batteries live longest if kept at a high or float charge so I don’t recommend them for a daily starting battery. The diode works toward the high side on my OEM battery but a bonus is my halogens shine much brighter!