Ongoing Combo Meter Hell

My 2005 Prius died a number of times in the last two months because it apparently was not turning off when we hit the power button.

I took the aftermarket battery to have a charge capacity test and it came back as working fine.

So it "seemed obvious" that it was the combo meter. Given that I could buy a rebuilt combo meter off ebay for the price of a diagnostic around here, I bought one and installed it myself, because who wouldn't.

However I am screwed.

The car would not start. If pressing the brake, nothing happened. If not pressing the brake, I would get the power light on green, a flashing light on the park button, and nada else other than the door open light up next to the combo meter.

So I took it all apart again, checked all the connections (from memory: two ribbon cables and two white connectors, one large one small on the combo meter; above steering wheel: two white connectors and one single wire grey connector, power button connector, park light connector in the air vent piece, two white connectors at top of center display unit and two connector at the bottom of it; one speaker cable above center console; one airbag connector on passenger side). Same deal.

Took it all apart a third time. reinstalled original combo meter which was working, just quit every once in a while. No change in symptoms, ie:

The car would not start. If pressing the brake, nothing happened. If not pressing the brake, I would get the power light on green, a flashing light on the park button, and nada else other than the door open light up next to the combo meter.

Obviously I am triple checking every connection every time, and I don't like tearing everything apart so many times, because these connectors are not the strongest.

As background, I feel competent to do this, I have done many pc and laptop repairs, arduino builds, random electronic repairs, car repairs, etc.

What next?

 

My battery was at 12.8 V last test. I will check fuses and disconnect battery and let you know where we are at.

 

OK, so it was a battery issue. I had checked voltage 2 days earlier and it was fine, and car was "off" for those two days, but somehow battery was dead. Other than the extended store test of battery health (which I did) and just waiting, is there any way I can proactively try to verify whether I have dealt with the battery drain issue? I did have a problem with the combo meter not dimming, which is fixed with the new one, as well as an issue with the headlights not turning off when turning off from aux mode (also fixed) - so perhaps I made the right guess.