Accidentally put negative to positive

I'm unable to copy diagrams for certain model years, and this is one of them, but regardless, this problem always has an easy solution. That output circuit is always protected on older cars with a fuse link wire in the harness, and on newer cars like yours by a large bolted-in fuse in the under-hood fuse box. Yours should be a 120-amp fuse near the battery.

Often other circuits tap off after that fuse so it protects more than just a shorted generator. Check that fuse, then let me know if we have to dig further.

Measure the voltage on both sides of it. There should be 12 volts on both sides at all times. If you have that, check for that 12 volts right on the large output stud on the generator. That should also be there all the time.

I know those large fuses have clear covers so you can do a visual check, but I've been an electrical specialist for over 45 years, and even I have trouble with most of those.

Another common problem is the smaller battery positive wire becomes loose under the nut that bolts it to the under-hood fuse box. On most car models that causes everything to be dead, or the dash lights turn on, then go off as soon as you try to crank the engine. If that was about to happen to your car within the next few months, accidentally grounding the generator's output terminal could have stressed what remained of that electrical connection to the point that high current couldn't pass, and the last of the connection arced away. In real bad cases you'd need to take that wire off and shine up the terminal. More often all that is needed is to tighten that nut.

The same symptom can occur if the smaller negative battery wire is rusted off where it bolts to the body sheet metal. That would be more common on a car the age of yours that gets slopped full of salt in winter.

It sounds like you're working with a vehicle that was attacked by a not-proficient do-it-yourselfer. As such, there's no easy way to figure out what might be messed up, but I can share at least one comment of value.

The Engine Computer can detect over 2,000 defects and set diagnostic fault codes for each of them. There can be over a dozen codes for just one sensor, for example, and they mean very different things. The important point to be aware of is of all those codes, only those things that could potentially have an adverse effect on emissions are the codes that turn on the Check Engine light. About half of the codes do not turn that light on, so you need to read and record the codes regardless if the light is on or not.

The people at many auto parts stores will read the codes for you for free. Once you know them, you can go here to see the definitions:

https://www.2carpros.com/trouble_codes/obd2/p0400

or I can interpret them for you. That said, I did see you had the codes read already, so I'm going to have to think about this a while. You might consider attaching a fuel pressure gauge and hooking it to the radio antenna or under a wiper arm so you can see what happens when the problem acts up. Part of what you described can be caused by a plugged strainer, or screen on the pick-up assembly on the fuel pump. It will cause problems when the largest volume of fuel is being pumped, . . . which is during coasting.

To verify that, use a test light or digital voltmeter. Put one probe on the battery's negative post, and the other one right on an unpainted bare surface on the engine or transmission. You should find 0.00 volts because electrically, those two points are the same point in the circuit. If the fat ground wire is not connected to the engine, or that cable is badly corroded under the insulation near the end where you can't see it easily, you'll find 12 volts. If you find anything other than 0 volts, suspect that cable. If you do find 0 volts, check it again while a helper tries to crank the engine. If some voltage appears, that also points to a problem with that cable.

There will also be a smaller wire connected to the battery's negative post that bolts to the body sheet metal. That will also cause a no-crank condition if it is disconnected, broken, or rusted off, but in addition, the lights and other stuff on the car won't work or won't work properly.