In 2018, I made a little readout box so I could see what the voltages were from the battery, panels, battery at the charge controller (so I could tell if there was a problem with the battery wires), and at "Load" on the controller.
These little digital volt meter (DVM) mulit-colored readouts are cheap on Amazon or eBay:
Colored LED DVMs
Mounting the readouts and switches behind the clear cover of the box:
Solar Panel Readout Construction 1 – 11/5/2018
Back then the kitchen table was my electronics bench.
Kitchen table electronics bench
The LED readouts and toggle switches for them get mounted in the box and wired up:
Wiring up the LED readouts
Here was the charge controller at the time:
SunSaver Charge Controller
All together, on the bench:
Solar Readout all together, on bench
Fire it up! Connected to solar system:
Solar Readout hooked up
Hey, this reminded my nephew of the electronics in the Back To The Future vehicle, haha. I'm just missing a Flux Capacitor:
Back To The Future readouts