89 volvo 240, Fuel gauge and temp gauge don't move. Also: sob story.

So back in the spring of 2016 I loaned my 240 to my dad, and then in November it stopped running.
I was busy, so I didn't have time to look at it, and then I had a moderate sized stroke. Weird I know, since i was only 29 at the time. I recovered, sort of, and in august me and my dad decided to fix it up. We got it running but we quickly realized that it had an issue charging the battery. We put a new alternator and battery in, but then my Dad died of cancer. So this story is partially about how life took a big **** on me, and partially about how my volvo did too. I'm like a **** magnet these days. Also it was about this time that we noticed neither the temp gauge or fuel gauge functioned at all. Neither one moves. Anyway, The other day I took it upon myself to make the damn thing run. I jumped it, but didn't check the battery, later on i found out that it's only putting out 2.65 volts. So in the process of driving the thing home, I trashed my alternator. Then the car died and I had to get it towed when I was halfway there. Luckily the battery and alternator were under warranty, so I replaced them both. Now the alternator is putting out 13.9 volts and that problem is solved. But I'm still trying to figure out why the temperature and fuel gauges stopped working simultaneously.

Any ideas?

Yes, you have had some issues!

I am not a later model specialist but earlier cars had a 10v (or 5v for real early cars) voltage regulator mounted on the back of the instrument cluster. The regulated voltage permitted more accurate meter readings than the wide variation of battery/alternator voltage.

That or the fuse or electrical connection from the fuse to the instrument panel.

Give it some acoustic tuning. (smack dash with fist.)

I have a known good used cluster voltage regulator. If this is a repair that you can do, I am happy to send it your way.

I had some crappy wiring be the culprit for me once.
I jiggled the wires around behind the dash and the gas/temp. gauges started working again immediately. It's not happened in 8 months so I'm not entirely sure what needs to be fixed.

I'd try it before getting a voltage regulator.

If you do need a regulator, you can also just buy a 7810 (LM7810, a common 10 volt linear voltage regulator) for a few cents and run a tiny bit of wire to swap the left and right pins, or mount it backwards and put a sheet of aluminum on the top to act as a new heat sink (pins 1 and 3 are swapped from the TCA700Y).
https://www.mouser.com/Search/Refine.aspx?Keyword=lm7810

If TWD's offering to give you one, you might as well take that though.