1st time owner/poster

Game: 1975 Bally Knockout. I've had it for a couple of months, and other than having to adjust a relay for the center kick-out hole, it's played fine.
Issue: I was playing a game and the play field & backglass lights suddenly went out. The machine still plays fine, insomuch as it keeps scores and every bumper/kickout/etc. still works. Just no lights at all.
Skills: Limited. I'm mechanically inclined, generally, but have no experience with reading schematics. I've soldered wires together before, but I've never soldered directly onto electrical components like boards.

I've seen forum posts suggesting that it could be a stuck tilt relay. But would I be correct to assume that a stuck tilt relay would cause the game to be in tilt, meaning it wouldn't otherwise function? I've also seen references to checking/cleaning the jones plug.

I've also looked at the fuses. There are spaces for 4 fuses, but only 3 are there. The 15A fuse is clearly blown. So that's my first guess of what to replace, but I don't want to go in the wrong direction and end up making bigger problems for myself. Funny thing about the blown fuse too, is that the wires are soldered directly onto the 15A fuse instead of onto the holder. The other 2 fuses that are present are hooked up like normal.

So I'm trying to make a checklist of what to do to troubleshoot the issue, any suggestions of where to start?

I was finally able to pick up a 15A fuse and get it put in last night, lights came back on. Glad I started small on the checklist before getting into a bigger mess.

Thank you all for the help.

Side note: Soldering in a small space inside of an old wooden box was not the most fun I've ever had. The Mrs wouldn't have let me live down burning down our house if things had gone sideways.