I'm driving across NC, playing in the snow, and my electrical system started cutting out. Found an open NTB, they said my alternator has died. 120k miles. No available part until Tuesday. Has anyone else run into this? Could it be a connection issue? Any help would be appreciated!

I doubt its a dead alternator if the electrical is cutting out. If it was the alternator, the battery would continue to run everything until it ran out of juice, which should be about 20-60 minutes (my guess on this, considering the amount of electronic stuff our 4runners have), depending on what battery you have and what you were using electrically during that time.

How exactly was it cutting out? Engine only? Lights? Dash? Everything at once?

Did it just cut out and not come back on again? Or, were you able to re-start it and continue on?

I bet its a loose connection somewhere, but will wait for a bit more info from you to really say. I know this has been covered before, but have no clue what thread it was.

It could appear to be cutting out, if the battery got to the ragged edge stuff would start flickering and dropping out one by one. Happened to me earlier this winter, ruined a trip into Capital Reef.

OP, do you have access to a multimeter? If you can get the truck jumpstarted and running even for a second, measure your voltage between the charge stud on the alternator and the negative stud on the battery. If that stays a solid 14ish volts, your alternator is probably good and you can look for a connection issue.

Lights, dash, blower fan, aftermarket GPS and radar detector, windshield wipers. They all cut off, but the engine never died.

They would fade out if a new load was added, but would come back on.

I have a multimeter. I'll see if it starts, check that, and report back.

I'm getting 13.9v at idle. Seems like nothing is wrong with the alternator. What else should I check?

Battery connectons. If you can move them at all they are loose.

Bad ECU? I believe that the dash etc runs on a separate one from the engine ECU. When you started the truck and measured 13.9v, did the cluster light up normally?

Check the battery connections and the battery quality /charge first.

Okki

How old is your battery?

This. Check your battery. You likely have a bad cell.

From past practice, if you had a bad cell, one would have trouble staring the vehicle unless jumped off.
But a battery check would be the fist place to start since your alt is producing 13.9V

Battery check was okay. Battery was in great shape. It's only a couple years old and no prior issues. I'll check the connections and see. I don't recall any play in the terminal connections.

Muddy, when my 2010 limited electrical started acting up, 4 wheel drive stuck in low while driving in high in a parking garage, 120,000 miles and 6 mo. old battery, I had a corroded positive battery terminal which is replaceable. No problems since. My opinion is all electrical items must be maintained correctly. BG

Thanks BGunn. I'll check my battery terminals. Are there any other electrical connections that can come loose?

Your battery terminals are just one side of a connection, check the other side of the cables too. I don't know what all you've got under the hood of a 5th gen, but at a minimum you'll have a heavy gauge ground cable between the negative terminal and the motor (or to the fender, and then the motor), and a heavy gauge power wire between the positive stud on the battery and the alternator charge post, and at least one lighter gauge power wire between the positive stud on the battery and the fuse box or boxes. Check them all, clean the connections really well.