Electrical issues

[Pickles]

hey everyone, been away a longgg while, but now I've got an issue thats got me pulling my hair out and I dont know what to do. I'll give a quick breakdown of the issues
First issue is that the dome light quit working, no power there for a couple months, fuse is fine
Next thing that happened after the dome light was the speedometer, radio, and heater control lights would randomly dim. Replaced dimmer switch, didnt fix it.
Then the speedo backlight totally quit working. I used a scan gauge 2 to monitor my speed so I wasn't really too concerned about night driving
And then about 2 days ago, the obd2 port stopped working along with all the dash gauges (check engine light, blinkers, TPMS light, airbag light all still work)
So far I've replaced both fuseboxes, the speedometer itself, the dimmer switch and double checked every fuse. Sometimes the gauges will randomly work for a second while driving but the majority of the time I get nothing. Ive examined all the wiring I could without ripping the entire dash out and found no issues. The thing I'm leaning towards at this point is the onstar/vicm module under the seat. Thats the next part I throw at it. Anyone have any suggestions other than that? I'm at a total loss with this thing

[Pickles]

also, side note, these issues were all spaced roughly 1-2 months apart, it just got progressively worse and worse

[OscUd]

I know this might seem simple, but have you checked what your battery's voltages are with the engine on and off?

It may be a good idea to check the voltage of your car's battery. One time my car (09 Aveo) had a loose bolt that connects the alternator wire to the positive terminal. This caused my battery to run low on voltage because the connector wasn't transferring any charge to the battery. As the car's battery ran out of charge over the course of one drive, certain lights like the ABS light came on and off, the dashboard would dim, certain parts of the car stopped working, like the speedometer, the fuel tank level gauge, the radio, and ultimately the car shut off and stopped working on its own. Tightening that bolt fixed my problem. If the alternator or the connection of the battery to alternator is bad then the battery can get either reduced or no charge from the alternator, which could result in electrical components not working. A lot of the symptoms I had on that particular drive are similar to the ones you had. I'm no expert and am not 100% certain, but I would check the battery voltage.

To check, use a voltmeter or multimeter. Remember red is +, black is -. Set the voltage setting on the multimeter/voltmeter to DC 20 V. With engine off, check the voltage; it should be around 12.6 V (this is with the engine cold. If it was recently driven, turn the high beams on for 10 secs, turn off, and wait 2 mins before measuring). With the engine on, the voltage should be between 13.5 V and 15 V. Note that by "engine on", I am referring to having started the car's ignition, not just having the key in the on position but the ignition off.

If the voltage is lower than 13.5 V with the engine on, then:
1) there is a loose connection between your alternator and battery
or
2) your alternator is probably not supplying enough charge to your battery and should be replaced

I don't think you'll have this problem, but if the voltage is greater than 15 V with engine on, then the alternator probably needs to be replaced due to a faulty voltage regulator.

I got the above procedures from my Haynes Repair Manual for Chevy Aveos

Good luck, I hope you can fix your car! Let us know if you have any updates.