Intermitten Alternator Failure

2003 Tacoma 3.4 TRD 220k miles. Mods: trailer breaks (did not install but bought it with them) led plug and play headlights.

Brief history: Battery(1) 3 months ago died. checked battery connections, ground wire loose. next three months cheepo battery terminals getting loose, battery light intermittenly going off and on (driving 70 miles a day). load tested battery and alternator sever times at orielies both check out fine. coming home from work battery died, had to push start it, went 2 miles then died again. got a jump was able to drive 40 miles home. pulled battery and got it tested and it was bad. battery #1 was 3 months old under warranty. drove with battery #2 for 20 minutes with 100% charge came home and it was at 70% with a battery light on. got new terminals again upgraded the connections to the terminals and put a thicker ground from battery to fender.

So obviously why not go out and get another denso alternator? the previous one is original and i have 200,000+ miles on it but hear about people getting 300,000 on theirs putting new brushes in ect. well just testing the alternator today with a multi meter and with the engine off im getting 12.43v and 14.25v with the truck on at 2,000rmp's. this was true when testing volts with the positive probe from the battery and from the B post on the alternator while putting the negative probe to the negative terminal, engine block, and other grounding locations.

This is telling me that my alternator works but not all the time. 2nd test we had 12volts with the truck off, turned it on its went to 14.28 but at some random time it dropped to 11.28v and had a light come on. (which is what im assuming happens when driving) gave it some time and now its totally fine.

I can totally afford to go out and buy a new alternator and I easily install a new alternator but we are all on Toyota World to learn how things work and to save some money. I dont know much about electrical issues but I would like some stories or pointers on what would cause inttermitten alternator problems. best case senario is that I need new brushes on my alternator worst case my ECU is crap. First time posing to T.W. got tired of searching through unrelated threads.

BTW if this hasn't been solved yet Im getting a lot of my troubleshooting help from this very informative video so if your just as lost as I am check it out and maybe you can get to my level of understanding. thanks for any help I appreciate it! ROCK ON!
https://youtu.be/1bK0De9XOP0

 

You can buy the brushes that come in the plastic housing for $20 or less from the dealership.
Just replaced mine two days ago.
That should fix your problem,

Do it before they short out the alternator and then you will have to replace the complete alternator, if it’s a Toyota alternator, that’s what you want

 

I'm thinking putting new brushes would be a good idea. There is a bunch of oil spilled in the alternator. I couldn't get a good picture of it too but the positive connector had some gunk in it but again the voltage test was good before I took it apart. Drove it 15 minutes with the light off untill it turned on. I know that temperature is important too. What would you say is a sign of the alternator shorting out? Going to pick up new brushes tomorrow. Thanks for the quick reply btw

 

^^^ this is with the cover off

 

Why is this alternator oil soaked?

I’m thinking that’s not good for an electrical path of current and that might be your problem

 

while it is possible to disassemble and do component testing of the alterntor the issue is where are you going to get the components? The intermitant operation of the alternator to me points to a alternator heat related failure, that means diode to me.

 

I think the oil is from a bad oil cap, going to get a new one....topic for another thread. but think your right on the over heating issue. the brushes definitely are toast but the commutator (the part that the brushes contact to) is kinda warn out + reads .8 ohms instead of 2.7 ohms like stated in the video. at this point I'm getting a rebuilt denso ordered since my truck has been sitting for 2 weeks. If I do go for cleaning the alternator I have found rebuild kits. idk doing the brushes sounded really easy but if the continuity test of the rest of the components are bad is it worth it to rebuild or just bite the bullet and get something that I know will work. hopefully this helps anyone reading this.