HELP! My truck is burning through alternators

So to begin, I have a 2020 Tacoma with the V6. It's been under surgery since May of last year.

The front wheel wells were cut out in order to fit larger tires, in relation to that the battery has been relocated to the back of the cab.

I am running a Optima Red Top battery

All stock grounds were kept.

In October, I finally went to go drive it and the alternator as shit the bed about 15 miles into the drive.

I limp it back to my shop and it's been sitting/getting worked on since.

Since then the red top battery has been on a trickle charger and has been holding a charge, but it has not been load tested.

This past weekend I finally installed a new to me alternator (it was taken off a totaled truck with 60k miles, but it was load tested prior to install)

I installed it and the truck was running perfectly for about 15 miles till the same shit happened. The truck lost all power and died on the side of the freeway.

I had it towed to a repair shop where it is currently getting diagnosed.

They are having a hard time finding what is wrong with it.

Any experience the same shit? In my opinion there has to be a short or a missing ground somewhere that is just killing the alternators back to back.

I have not been able to spot any affected harnesses or anything with my inspection.

Here are some pictures for you guys


Battery relocation. Using distribution blocks, so all stock grounds were kept.

Inner fenders cut

Sitting at the repair shop

 

Did it die at the same place? Maybe that same bump? major changes don’t always result in the intended result. I’d check then add a ground closer to the battery

 

Is there a way to test the alternator output? Coincidence second one was bad but not if both sat a long time. Maybe got bad spot in the brushes or contacts from sitting?

The 15 min may just be what it takes to run the battery down without the alternator recharging it.

 

I would suggest starting with a complete system test meaning with a wiring diagram, back probe and check for signal to the alternator telling it to charge and then do a voltage drop over the alternator B+ to battery positive and then ground to alternator case to see whats missing. check the wiring diagram because the signal circuit could be 12volts or 5 volts. Idk. The positive and negative voltage drop tests should be basically zero volts or close to it. If either one of those two voltage drop tests shows significant/ system voltage then you have an open or disconnected cable somewhere.

Of course all these tests should be done with the engine running. You'll find the direction you need to go from there.

 

Just get a second alternator.

Then alternate your alternators.

 

Don’t you have to change a setting in the ecm when you change to AGM battery

 

How many amps is the battery rated for. Since you relocated battery. May need bigger cables going to battery..

 

I'm using 1 gauge wire

 

I've heard about this but I've also read about people that have no issues not changing anything

 

Saw this, maybe there is some information that may help.


https://youtu.be/89Jchhl0oOQ



A multimeter could be used to check both battery and alternator output. According to this video these battery’s have a higher charging requirement.

Good luck, Woodcutter

 

If there is a reputable electrical specialty shop in your area that rebuilds things like alternators, generators, starters, and other electrical motors, that's where I'd be headed.

Shop I use (rarely, thankfully) are masters at that stuff.

 

How is the alternator dying? Is it overheated and burnt? Fine but not just not outputting? How does it test after dying?

The glaring item here that I would first suspect is at play is the battery relocation. I think the most likely culprit would be something to do w/ the voltage sensing that controls the alternator output. Typically you want this sensed as close to the actual battery as possible to get the most precise battery voltage reading. It's possible the electronic controller for this is very sensitive to this value and small voltage drops.

To verify, I would run a test w/ the battery back in the stock location to isolate the issue to being due to the relocation.

 

It just doesn't push enough voltage with the stock settings to FULLY charge most AGMs. For most people that's perfectly fine and you'd never know the difference. You'll just get a bit more capacity outta your battery with the higher setting. My resting voltage was a good amount higher after doing a voltage increase mod in my 2nd gen, much easier with the 3rd gen being able to change it with a tune.

 

You should, but it won't kill one in 15 miles if you don't. They just like slightly higher voltage.

OP is the battery new with this setup? If not, how old is it?

 

I just got a call from the shop.

They stated that the alternator is putting out power, however the harness that plugs into the alternator is having issues. They said they can move the harness and get a different voltage reading.

I gave them the go ahead to tear into the harness and see if they can fix the mess

 

It was brand new purchased in September of 2024

 

Can you get that swapped out? Could have a bad cell.

Just saw this. Hopefully that is it.

 

The video is for 2nd gens, this is a 3rd gen question. The 3rd gen alternator receives a digital signal (LIN) from the BCM.

 

Problem has been found. Shop said the alternator was actually fine, putting out 14.2 volts but at the distribution blocks it was 4 volts.

They chased the harness all over the truck and hours later they found where the harness ended

Because it became apart of a bunch of different harnesses they found a loose nut grounding the wires

I'm kinda pissed that I paid someone to tell me a ground was lose but I didn't have time to chase that shit down.

 

Please have them show you where the culprit ground was and take pictures to show others where the problem could possibly be.