I've had a G4 Mac mini with a bad firewire for a while. I want to try a few things, but I figured someone might know a bit about it ahead of me trying anything. I understand that this is not an uncommon problem with these, but I'm unsure what causes it. Anyone have any insight? I'm not beyond replacing components if I can identify them.

Define "bad FireWire." Unfortunately, you're probably looking at a logic board swap. I had a mini that ate its ATA controller and that was about all you could do (no slots to get around the problem).

I'll have to check to see what exactly the issue is, its been a minute, but I don't think Firewire devices were even receiving power. I think the System Report still saw Firewire hardware. I'm not against doing board work, if the controller is the issue. I suppose I'm getting ahead of myself, but I'm also wondering what other people have seen.

If it's just a power issue, one way to work around that is to get a powered FireWire hub, plug the Mac into that, and plug your devices into the hub. The hub will provide them power. The Belkins aren't very expensive used, so that may be an easy way to diagnose the problem better. See also https://oldvcr.blogspot.com/2021/06/the-parallel-universe-of-firewire-hubs.html