I made the mistake of contemplating what the old gal might be worth in today's crazy used vehicle market and almost immediately the dash lit up with just about every light aside from the CEL. I was going about 50 but the speedo needle was swinging up and down wildly. The ABS and traction control lights along with e-brake light came on first, I believe. Hopefully it is something as simple as a speed or ABS sensor but the dash went dead eventually. It only seemed to have a minor effect on the engine and tranny but the windows would not work and the wipers barely moved. The battery is not that old but that light was on too. Possibly alternator? I was going to buy a used one but my friend talked me out of it due to how reliable this thing has been. Ideas?

These symptoms are common when the ground connections are bad. Start with the negative cable on the battery; make sure it is clean and tight. Then the negative cable where it attaches to the body or motor. Then. check any grounding terminals you can find on the chassis and behind the dash.

I doubt it is any relay, control box, alternator, or battery, etc. It has always been a bad ground when I have had that problem.

Hope it's not rodents chewing wiring.

Thanks, I will check that. The only thing I have done recently was the coolant and oil change but I did not touch the battery cables. I found a low mile alternator off a 2018 for $75 so I bought for a spare if this one is still good. The truck would not start after I parked it so I can't test the alternator.

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Nothing obviously loose. Some minor acid scale on top of the battery by hold down clamp but terminals looked good. I have the battery on the charger right now to check if it will start later.

We drive it almost daily even with working from home so I doubt it's rodents chewing wires.

ETA: Started up fine after charging battery and no lights on dash but died immediately when I pulled the negative cable. That alternator looks like it's in there real good. Fun times ahead.

I don’t think that’s a recommended method of testing an alternator on a modern computer-controlled vehicle.
What happens if I disconnect the battery while my car is running? - #18 by Kim_Bell - General Discussion - Car Talk Community

You are probably correct but I don't see how it's any worse than having the alternator go out while driving and having the dash look like a Christmas tree. Windows wouldn't even roll down.

I’d suspect the battery, or connections, first. The age of a battery isn’t the only indicator of its health.

Do you have a voltmeter?
After resting for a while, a fully charged battery should be about 12.6V.
If it’s 12.2V it’s about 50% discharged.

During starting a healthy car battery voltage should be 10v or higher.

The voltage, when the engine is running, should be in the range of 13.5-14.7 volts, indicating the alternator is doing it’s job.

You could also take it in to an auto parts store to have them load test it.

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In addition to what Electroboy says, I've found worn alternator brushes to cause problems. If you have an alternator in your hand, it's a matter of 5 minutes to get the brush assembly out for a visual inspection. Even a rebuild can have bad brushes.

Thanks for the info. Aside from the age of what I bought I am having second thoughts about a used alternator. Might buy a new one.

You should be able to get a Toyota reman at a dealership if you're near one. Less expensive than new but more than aftermarket. And again, brushes are cheap and easy. Best wishes!

I bought a new one for $300 at Bam Wholesale including overnight shipping. Decent price, IMO. A new one at a local dealer was $400.

If you add a part at Bam to your cart and go to checkout to fill in email and address it will send you a promo code for 20% off shipping if you don't place the order within an hour or so. Have to click proceed to payment section, etc.

QwikKotaTx - Did you ever figure this out to be the alternator?

I just tonight had this exact thing happen to me on my '10 SR5 - 40 mph, dash lit up, speedo moving all over the place, wipers very slow and then it died when I came to a stop. Electrical was still working but would not start.

I put in a new battery and it started right away, but the battery light remains on even though I was able to drive home.

My old battery had only a 7% charge left. Guy at Autozone said it is most likely the alternator sucking the battery down and not being able to recharge it.

That's a weird thing to say" alternator sucking down." I think your issue is the alternator is not charging the battery.

List price on a brand new (I’m assuming) alternator is $386 but using the Toyota Parts website you can find places that discount up to 30% or more. And you can use their free shipping offer right now.

2706031190 - Alternator. Battery, CONNECTOR, ACCESSORY - Genuine Toyota Part

Madera Toyota is one dealer near me that sells for $267.

2706031190 - Toyota Alternator. Battery, CONNECTOR, ACCESSORY | Madera Toyota, Madera CA

Also, I just noticed that Summit Racing is now offering rebuilt Denso alternators for our trucks. $140.
Unfortunately there’s a core charge so...not so great if you don’t have one close to you.

https://www.summitracing.com/parts/dnp-210-1190