Hey all, I've been a long time lurker but have never actually started my own thread. I'm in desperate need of help, so the time has finally arrived.
My car's been making an ugly grinding noise the past week. With visual inspections, I found nothing wrong. But last Friday it cranked and immediately died. I popped the hood and the negative terminal and connection were fusing together so I quickly popped off both positive and negative connections. I assumed it was something wrong with the battery, so I replaced it. Upon putting in the new battery, it sizzled both terminals/posts again so I quickly pried them off.
I suspected the starter, so I took that out and it was very, verk broken. In fact, the starter pinion was lodged in the flex plate (my 4Runner's an automatic). I cranked the engine pulley a turn which freed up the pinion.
I carried on and put in a new Denso starter (#2800166) yesterday. The 4Runner started up, made the same ugly grinding noise as before the swap, and the starter promptly started smoking.
I'm no mechanic-- this is my first car and it has slowly been turning me into a "car guy", but I have very little experience, so any and all help is appreciated.
I assume it's an electrical issue but I'm lost. I have found no ground issues or wiring issues in general.
Thanks for taking the time to read and for any help!

Edit-- if helpful at all: 4Runner is a 2000 SR5 automatic that just hit 202k miles

Check the ground wires.3 ground wires, one from the Driver side inner fender to the negative battery post, one from the firewall to the back of the head and one from the negative battery post to the block. Then check wiring harness going to the alternator for shorts or exposed wire do the same with the starter wires and connectors.

Thanks for the response! I checked the three main ground wires, nothing suspicious there. I can't find any loose or exposed wires coming to/from the alternator or starter either. All the mechanic shops are at least two weeks out right now, and I've heard mechanics are not great with wiring anyway. I'm having a hard time being optimistic!

@RomanSchnobrich did you get this resolved?

@cl4Rk I did, but it was puzzling (and expensive) to solve. Replacing the starter took care of the electrical issues, but there were still gnarly grinding noises. I had an independent mechanic drop my transmission and replace my flex plate with a new OEM one. After all that and a new transfer case leak my 4Runner is back to normal. No electrical and no starting issues, and no leaks.
Are you going through something similar?

No I'm not. I did have to replace my starter and starter relay earlier this year, but I was mostly curious if your grinding noise was related or just a coincidence.

Good! Yeah I'm annoyed with myself that I just ignored the grinding for so long. I'm sure that's what ended up snapping off/grinding down so many of the flexplate's teeth. From my understanding, the ugly grinding was absolutely the starter pinion engaging/disengaging with the flexplate incorrectly and not getting addressed sooner.