Charging System Issue

These aftermarket painted terminals are complete junk ive delt with these not allowing voltage to pass through. I would replace that terminal first and the ground one if its painted too.

 

You need to turn the alternator "on" for it to work.
You need to have a "good" charge sensing circuit to regulate the current/voltage of the alternator.
You need a good path to the battery for charging.
.
I would GUESS you have an issue with something not turning the alternator on, or you have something preventing the alternator from charging fully. (resistance)

I haven't seen anyone ask what the battery voltage is when the light is On and OFF. This should be EASY.

This issue shouldn't be "hard" diagnose. Guessing will only make it harder/

Step 1. Learn how the charging system works.
http://wilbo666.pbworks.com/w/page/39441708/Toyota Alternators

Step 2. Lean how to do a basic voltage drop and resistance test.
https://autoprollc.com/wp-content/uploads/2016/12/2-Voltage_RemyTechnicalBulletin_Dec2015_web.pdf

Step 3. Diagnose your issue.








Diagram

 

Please disconnect the battery before fiddling around with this stuff, I know of an incident that literally took the top of a guy's head off when he opened the hood.

Yes, upgrading the post terminals could be the entire problem.

I'm not disagreeing with you, but "one time" I was walking distance to an AutoZone and the Taco was my only ride. I cleaned up the wires and put two of these squish-type terminals on out of necessity. (Unpainted, but still crap.) They've been fine ever since, that was in 2018 (for posterity, it's now 2024.)

I have a military style post kit arriving today, complete with copper crimps. Just one of those projects I never got around to because it wasn't broken.

 

understood

 

Still haven't figured the issue out. Last night i replaced the stock alternator wire with a new 4ga wire from the alternator post to the post in the fuse box. I only have a couple more ideas before I'm defeated. I'm going to replace the pigtail harness the goes to the alternator and I'm going to replace some ground wires too. I need to trace the ground wire from the 4 wire pigtail that plugs into the fuse box from the 3 wire pigtail that comes from the alternator. other than that I'm stumped. all the fuses are fine all the positive wires are good. I put a new negative wire from the battery and grounded it to the body. maybe I'll replace the ground wire that goes from the engine to the battery as well. At this point I don't know anything else that would cause this, the alternator is brand new so I doubt its faulty. The main thing that is irritating me is i had it working perfectly at one point and as soon as I tried to make it a cleaner install it cause all these problems.

 

There isn't a ground wire that plugs into the alternator.
The alternator is grounded through the block.

 

I was talking about the black wire that comes out of the 4 wire pigtail that goes into the fuse box, the one that the alternator pigtail leads into. Although I was just assuming it was a ground because of it being a black wire.

 

So after buying a multimeter

I bought a multimeter and followed this. If I'm understanding correctly it may be a grounding issue.

 

Multimeter hooked up to battery positive on positive and negative on negative it averages about 14.3 volts, positive lead of multimeter on alternators positive post and negative on batteries negative terminal is also about 14.3 volts. But positive of multimeter on positive of alternator and negative of multimeter on positive of battery is 0.02 volts so that suggests a ground issue if I'm correct, right?

 

What readings did you get to make you think its a ground issue?
Did you test from the battery terminal ground and then to the block and have different readings?

 

No, you'd be checking a voltage drop on the POSITVE wire that way.
.02v is great.

Electricity flows the path of least resistance.
If you're meter read .5v or more than you'd have an issue.

 

Where did you buy the alternator from? If Autozone I would definitely question the new alternator.

I'd recommend getting a new denso or even a reman. Denso from rockauto. Anything but an autozone alternator.

 

ok understood, in that case then everything seems to be within spec. But the battery tester they have at AutoZone keeps saying bad charging system. I also checked the 7.5A ALT-S fuse and that also came back at 14.2v so I'm not sure if their tester is just wrong. My battery is charging and there isn't a drain somewhere because I tested the voltage at the end of the day and then first thing in the morning and it was 12v both times. The voltage reader on my aftermarket radio does fluctuate from 14.2v to 13.6 and everywhere inbetween. But I'm sure it's not very accurate seeing as it will say its 13.8v but when I check the battery with the multimeter it reads out 14.3.

 

EBay I can see there being red flags there lol but from what I can see from the multimeter the alternator seems to be working and I had this problem before I replaced the alternator so now I'm not even sure if my old one was bad. If the alternator is the case I know eBay has the return policy through eBay motors so I will be reimbursed.

 

Ok. Well with my experience I wouldn't trust it. Just me though.

I know you said Autozone test failed. But is your battery light coming on? Is your battery actually dying?

 

The battery light was coming on at one point. The truck was being lightly driven for a couple months (like once every 2-3 days for like 15-20 tops) I'd start the truck the light would be on for a few minutes or until I drove it for about 100ft then would go off. The battery was pretty old and the terminals were getting pretty corroded so I replaced the battery and had autozone test charging system for the hell of it, it came back back so that sent me down this rabbit hole. I've been driving everyday for extended periods of time now and the light hasn't come back on but the test still says bad charging system, yet when I test it everything seems to be within spec. My main worry is prematurely wearing out the new alternator or battery.

 

I have experienced charging "issues" after wiring upgrade and alternator upgrade.

So, having learned to start simple:

When the light comes on, what voltage is the alternator actually putting out? (Is it possible the charge warning circuit itself is the issue and not your actual charging system?)

triple check the harness connection at the fuse block - I had thought I did, but turns out it was not fully plugged in (my problem solved).

All the best in getting a handle on your issue.

 

I'm pretty sure the harness is fully plugged in but like you said I will triple check, I will feel pretty stupid if that was the issue lol. Either way everything I've been doing needs to be done after upgrading an alternator anyway, short of 1 or 2 wires I've pretty much replaced the entire charging system at this point.

 

That black wire is not a ground, it is the start trigger wire, it applies 12v to starter solenoid when key is rotated to start.

 

Ok understood that makes a lot of sense, that saves me the time tracing that wire then lol. Do you happen to know the part number for that 4 wire pigtail?