2tr-fe all coils code, low voltage at coil

Nice work figuring it out. As said, you need to use a test light- unless you get no voltage. The DMM might show 12V, but the circuit may only allow .01A- you need to add a 1-2A test light in series to make sure there is sufficient amperage.

That last pic looks like one of those "magic" butt splice connectors that melts the internal solder- no for me. Any of those HF looking butt connectors should make your warning light go off.

 

Only after fixing it did I understand the need for a test light and how actual load would have given me a clearer picture. Adding that to the list of tools to buy, lol.

It’s a crimp of sorts - it has a thick metal sleeve surrounded by shrink plastic shielding. They must’ve cut thru the shielding when they crimped it, giving the metal an opportunity to bleed voltage. I’m not even sure why the crimp was there as there wasn’t any evidence of it being connected to something previously. The prev owner had aftermarket stereo and alarm stuff installed and they kinda did a hack job of it; over the years I’ve had to undo and redo a lot of the wiring. Here’s an example of what I found behind the head unit when I first bought the truck:

 

I see crap like that all the time with aftermarket installs, my favorite is always the unfused mystery wire coming directly from the positive battery terminal going around through the door jamb to somewhere inside. That more vehicles don't just randomly light on fire because of a short from crap like that is beyond me, I'm sorry but some people just shouldn't be allowed around wiring