[RedDevil]

The meter failure and IMA warning were probably caused by feeding the internal volt meter with 12V from the car.
I bet the IMA system does not like to be connected to the 12V system in any way, like if the meter has a common ground or something.
That did not reveal in my bench tests (where I used a separate 12V source).

I will check on the volt meter this evening.
If it still functions I'll hook it up with a separate 12V source. I have a bunch of tiny 12V batteries (half the size of an AAA pencil battery) and will use that plus a switch as the source. And I'll put some 2K2 Ohm resistors in the test leads just to be sure.
As often in my life, wisdom comes from messing things up first.

Oh, and the car behaved fine this morning. In fact better than usual, partly due to me booting it a little in my second test drive yesterday evening, so the IMA battery must have held a higher state of charge than usual.
That effect of a higher SOC motivates me even more to get the pack sorted out and operational.