You are a freaking genius. It was an Electrum wallet and after testing a few passwords, I found the correct one and the balance was...0 BTC. Anyway, thanks a lot for helping!
Let me ask you a related question. I also have a couple of old wallets for ripple, most likely with $0 balance as well, but just in case. These are files that have a long string that starts with:
eyJpdiI6IktqTVJKOG and continues
How would I restore these?