Few months back battery light and brake lights come on and get my battery and alt. tested to find out my alt. is bad. So I changed that. Last week battery light comes on again so I go in and get my battery tested and it's bad so I bought a new one as well. When I first started it with the new battery, the battery light was still on even after I drove around for a bit so I figured maybe I have to reset my ECU. I did and my battery light when off. About a week later it's back on? I was going to go get my alt. and battery tested again but has this happened to anyone else?

I'm going to go ahead and reset my ECU again to see if it happens still but what could be causing this?

 

check the fuse block behind the battery for corrosion on the terminals.
sometimes, just loosening and tightening connection can help so check around the alternator too.

 

I had this problem, then the main ground wire post broke off of my bosch replacement alternator.. Luckily there was enough stud left for me to bolt the thing back together.

 

Yikes, I think there is a rule against putting bosch stuff on a yota. Not the best rep in here for electrical stuff. You should have 14.something volts with the truck running at the battery. After sitting a day or two should still have 13.something at the battery. All the wires are suspect too. Seem to break/corrode easily with all the years on them.

 

Sounds like you have some bad connections

The B terminal wire of the alternator could be cooked from the thermal cycling after all these years.

The plug on the alternator could be corroded

Besides removing the battery cables does reset the ECU interesting why it turned the charge light off