Update: I found an engine head stud within range of the existing ground wire boot. No splicing/replacing needed. Hasn't stalled again yet but planning on installing the new alternator boot Monday..

Hello all, if anyone could give me some confirmation or ideas of other causes for my electrical issue I would really appreciate it. My wife' second-hand 2000 Mercury Grand Marquis (125k miles) has died while driving three times. The first time it happened she said the engine just died, and the steering locked up but she was able to make it off to the right side. Before I could ask for any lights on the dash, she had turned the car off. When she tried to restart it, it ran again without any dash lights coming on. That was about a year ago.

Two days ago, I was driving it and it did the same thing. The power never went completely out because the radio and dash instruments still worked. But the power steering worked for a couple seconds and the brakes were hard. I put it in park and left the key in the on position and noted the check engine light and battery light were on, not flashing. I opened the hood to check for a loose battery connection or harness connection but couldn't find anything. I put the key in the off position, then restarted the engine. The check engine and battery light were off, and I drove it home.

Today it happened again when going in reverse out of a parking spot. The same lights turned on. I put it in park, left the key in the on position and used a friends car to borrow an obd II scanner from Advance Auto Parts. But by the time I got back, my wife had turned it off. We turned it back on, the dash lights were off again, and we drove home.

I've done a little research and I think I have three educated guesses since we haven't been able to retrieve a code yet.
1) The boot over the alternator wire is mostly missing. The eyelet and wire don't look corroded or damaged. Could a damaged boot cause a "short circuit" like that?

2) I replaced the original coolant intake manifold with an aftermarket coolant intake manifold 2 weeks ago. One of the old manifold screws had a stud with a black ground wire attached to it, by a boot. But the new after market manifold uses new self tapping screws without studs, and the ground wire boot can't attach. The wire was too short to reach anything else and I just left it hang. I've read that faulty electrical ground can cause a car to stall while driving. It seems like if this was a safety feature, the design would be to keep the car from starting in the first place, not to have it stall while driving. The first time the stall happened the ground was attached to something, so it doesn't seem to be the right cause.

3) I've read that faulty fuel pumps can cause sudden stalls. But I don't think that would cause a battery light to turn on, would it?

I'm ordering a replacement alternator boot on amazon tonight. I'm also going to find another stud near the loose ground wire and splice a longer ground wire in to reach it. Can anyone give me some advice?

Thanks so much and Happy New Year