The other issue you're likely to run into is CAT5 is usually solid core wire (non-stranded). It will work ok as far as lamps or input switches... do not use it for coils. Solid wire doesn't hold up well to vibrations and flexing so it's also likely to break over time. Also, it doesn't take solder as nicely as tinned multi-strand wire. You can find plenty of 22-24 AWG multi-strand wire on Amazon at a reasonable price. Mouser Electric and Grainger are also good sources.

I personally wouldn't use it due to the vibration / breakage issue.
But... that's just me.

G

Just another thought... you could search on Mr. Pinball Classifieds for anyone getting rid of old pinball wiring harness. I've seen them go really cheap. You'll have a complete selection of properly sized wire for pinball purposes with the usual colors (depending on manufacturer). Not sure if anyone is getting rid of any right now. Saw a Bally Mystic harness about a month ago... if he still has it.

Just an option

Actually... just checked ebay has some also.