They're old, they're ... experienced...

But they still work if you actually wire them to something.

Yesterday I scored some like-new 12 gauge multistrand wire. This morning before it got too hot I tore out all the Dr. Seuss wiring that theoretically but not really united my scrounged solar panels into a harmonious whole and re-wired them correctly. Found two hidden bad connections. Ditched a multitude of wire nuts.

Voltage is still low, of course, and I really do need to score some new batteries and a charge controller. But the whole system immediately started working a lot better. The inverter is no longer screaming at me.

Never assume you know why something you barely understand isn't working, until you actually check to see if you can find out.