Keep getting non base-58 character error when trying to recover my old wallet. Any ideas on how to troubleshoot this? Basically I made a purchase with bitcoins back in ~2014 and I remember that I had a little bit leftover. However all documentation I have is a file labelled wallet with a huge string of characters. But when I try and access it on any application I get the non base-58 character error. There are a bunch of +'s and /'s. Does anyone have any idea what I could try to see if this is it? Sorry for not having more advance knowledge.
There are a bunch of +'s and /'s.

That strongly suggests it is data in Base64 encoding. Note that, in this case encoding does not mean encryption, just a specific printable representation of binary data.

Does anyone have any idea what I could try to see if this is it?

It seems several different wallets might use Base64 encoding, including:

Blockchain.info backup using AES encrypted JSON

Bitcoin Wallet for Android (Schildbach wallet)

Print wallet.dat with base64


Of those, I'd guess the first is most likely. But that's just a guess. There are probably numerous other possibilities.
I think I'd try the Blockchain.info recovery process first then, if that didn't work, try decoding the file from Base64 into binary and using a hex editor to look for patterns that might give some clues to the software that produced it. If the file is encrypted using a wallet password this probably would not be fruitful.