I actually didn't replace the Cherry switch. I put an LED in it.
I got a 3mm red LED from GPE (P/N HLMP1700). I soldered the fine silicone wires to it, but I left the leads on it, which I heat shrinked. Keeping the leads on allowed me to bend and form it, so I could get it up into the button, similar to the normal-sized LED Cherrys. (The fire button Cherry is basically a shrunken version, with no LED.) I think I zip tied the LED wires to one of the other wires for the switch, to hold the LED up inside the button.
The silicone wire I use is pretty good stuff. Doesn't melt, and tough enough to be abrasion-resistant, but it's a dream to strip and work with, and it's super supple. I have all different gauges of it, which I've ordered from different places on ebay (all Chinese).
Not all sellers have the really good stuff, so I'll order a test batch, and if it's good, I order a larger bunch from that same seller, as I use it for everything. I think I used 28 or 30AWG in this case. The wire is thin and super flexible, but the core is made up of super-fine strands, and a lot of them. (The cheaper stuff is mostly insulation, with very few core strands).
The wires are fine enough, and they're not stuffed into the shaft, that there isn't much friction in there to cause issues, aside from getting the bolts through, which you just need to be careful with. (And it's my home use cab, so it's not getting a ton of play.) The way I routed the wires out of the bottom, they don't rub there either, again, not that I'm worried about abrasion.
Power was the trickier part. I didn't want to run a separate dedicated power wire all the way back to the AR, so I ended up using one of the lines for the unused center coin mech/slot on the coin door. I think it's 12V, I forget. There are a bunch of unused wires already with spade connectors on them, bunched together for the center coin slot. I just grabbed my meter and found one that was power.
The trickiest part (which I spent way too much time on) was figuring out the right resistor value to get the brightness right. You have to use a bigger one, as I was pulling from a 12V supply, instead of 5V, and it's a brighter LED than the ones from 30 years ago. I did the calculations, but it still ended up being too bright. I tried a bunch of different values, as I wanted to match the brightness to the start button. In the end, I said screw it, and threw a pot in there, so I could adjust the brightness (which is the one thing I'd recommend, if you're going to try it.)
It was a stupid project that took way more time than it should have, but I get a kick out of seeing that stupid little button lit up every time I play it. Lol.