Just found a complete wiring nightmare in a 40 year old garage

The crumbling insulation is the biggest red flag here because it means the heat has essentially baked the wire brittle over the last few decades. Once that rubber or plastic starts flaking off when you barely move it, there is no real way to save that section of wire. You can try to slide some **heat shrink tubing** over the individual conductors if you have enough slack, but if it's that bad inside the box, the stuff inside the wall or ceiling is likely just as toasted.

That ground wire wrapped around the hot lead is a special kind of death wish. It sounds like someone wanted to use the ground as a neutral or just had no clue what they were doing and got lucky it didn't short out imediately. If that connection had any resistance, it could have easily stayed hot enough to start a fire without ever drawing enough current to trip an old-school breaker. Garages are notorious for this stuff because people figure it’s just an outbuilding and doesn't need to follow code. I wouldn't even bother trying to salvage those connections. If you have access to the attic space or the studs are open, you shoud just pull it all out and run a fresh line. Modern garage door openers relly should be on their own dedicated 20-amp circuit anyway, expecially if you plan on running any power tools or a compressor in there at the same time. Trying to patch into 40-year-old creative wiring is just inheriting someone else's nightmare.

If you absolutely can't pull a new home run, you need to find the next junction box upstream where the wire is acutally still flexible and start from there. But given what you described with the chewed-up jacket and the paper showing, that whole run is compromised. Kill the breaker, pull it all out, and do it right with some 12/2 Romex so you can actually sleep at night.

Man, that crumbling insulation part sounds terrifying. Is that what happens to all old wires eventually, or is it just becasue of the heat from the bad connections? I’m working on a small project too and now I’m paranoid about checking my own boxes. When you mentioned the paper inside the cable, is that a specific brand or just how they made it back then? I’ve only ever seen the smooth plastic stuff in the new rolls at the store. definitly makes me want to double check my garage before I plug anything heavy in.

That paper is just standard for older Romex; it was there to stop the jacket from bonding to the conductors. If you're seeing it, that outer sheath is toast. Check the actual metal of the wire while you're at it—if it looks silvery instead of copper, you might be dealing with old tinned copper or even aluminum from the late 60s. Honestly, don't even try to save an inch of that. If the insulation is flaking off like dry leaves, the heat has compromised the integrity of the whole run. Pulling new 12/2 is the only way to be sure you won't have a glow-in-the-dark garage later.

That chewed-up jacket is a huge red flag for rodents. If mice have been at it in one spot, they've almost certainly gnawed on the wires deeper in the walls where you can't see them. Since you're allready in there, I'd just bite the bullet and run a dedicated circuit for the opener. Modern codes require GFCI protection in garages anyway, and those old hacked-in circuits usually won't play nice with a GFCI outlet. It's way cheaper to buy a roll of 12/2 than to deal with a short circuit inside a wall you just finished fixing up.

Since you're pulling that light fixture anyway, look at the box type. If it's an old metal one and they didn't ground the housing—and with that ground wire wrapped around the hot, I'd bet they didn't—the whole thing coud be live. I ran into a mess where the box was so overstuffed that the heat couldn't dissipate, which is likely why your insulation is flaking off like dry leaves. If you see any signs of arcing or soot on the back of the box, just rip it all out. Box fill limits exist for a reason, and hacking in extra lines usally ignores those completely.