2006 tundra not charging

I had the alternator changed, checked fuses and grounds. Put old alternator back on and it charged for a while. Now will not charge again. Any ideas?

 

Battery?

 

The Battery has been changed. Only voltage when at idle is the battery voltage. Checked plug for alternator and seems to be good.

 

If you went with an aftermarket/store brand alternator, aftermarket part quality has gone utterly down the shitter in the last 5-10 years. Like, insanely so. The number of DOA and early-fail products we see is astronomical, unacceptable.

If you didn't buy Denso (OEM) brand from a reputable (i.e. not scAmazon or fleaBay, where knockoffs are rampant), and didn't buy the replacement alternator direct from Toyota, consider pulling the alternator to have it bench tested at the local auto parts store. Most major chains test for free. Unless I'm misunderstanding what you're saying about swapping in/out alternators.

Inside-the-wire corrosion is common in these trucks. If you're 100% positive the alternator itself is good, if you don't have a DMM to test resistance on the alternator wire for issues, you could try running a temporary 4awg lead from the battery to the alternator and run that - the alternator gets two feeds, the plug/harness with smaller wires at the rear, and the jahunga power cable to the side IIRC.

Additionally, have you checked the state of the alternator/power related fuses in the fuse/relay box next to the battery?

This sounds like a classic case of corrosion in the battery cables. See here for what I mean (2nd pic): https://www.tundras.com/threads/1st-gen-psa-clean-your-battery-terminals-you-lazy-sods.131635/

 

I got the alternator checked at the auto store and it checked out good. And yes, I did try to do things the cheaper way and got an aftermarket. Lol. So with the original alternator on it was charging when I left the house and stopped charging after about 20 minutes down the road. Thanks for the input.

 

I don't know what cab type you have, but it's important. Fuseboxes differ across the years, and between cab types.

But generally speaking, you may have either (A) excess corrosion inside the heaviest cable, going from the positive battery terminal to the side of the alternator, (B) a short-out or rub-thru on that heavier-gauge wire between battery and alternator, OR in one of the smaller wires that's connected by harness to the back of the alternator, (C) a short/loose wire/fried fuse related to the short jumper that goes from the battery to the fusebox and/or a mini-fuse or window-fuse in the box next to the battery, or one of its connections underneath it, or (D) a bad ground somewhere, or (E) a faulty positive battery terminal, which happens with the shit OEM design Toyota chose IMHO.

Ultimately, running a temporary wire (properly secured of course, and proper gauge) between the positive battery post and the side of the alternator could rule out (A), (E) and some of (C), it won't rule out the others. (C) will one of two likely causes IMHO but hardest to debug. I doubt it's (D) but also have no history on your truck, and no picture of the engine bay to look at. Checking fuses is, in my opinion, the easiest 1st step you can take, but it's not blatantly obvious which fuses are related without knowing cab type. Especially with double cabs, the M-USB fuses can be confusing as hell for some people.