Each step took some part of a weekend; there were typically several months between each step State: 1970s house weirdly full of pre-1970s outlets (probably usi

Each step took some part of a weekend; there were typically several months between each step State: 1970s house weirdly full of pre-1970s outlets (probably using whatever the builder could get on the cheap). "Basement" bedrooms have AFCI that trips when using an 8 amp space heater. Circuit breaker is a generic "Fit any panel" model not specifically made for the panel. Outlets wired with a devil-may-care attitude where hot and neutral were both regarded as "makes sparks" and no outlets had grounds. Even though the branch is in a basement area and ends in a bathroom with an outlet right above a sink, there's no GFCI. * replace all the outlets in the circuit, put GFCI outlet on first outlet in the circuit. (still tripped with space heater); GFCI doesn't trip except when tested. * switch circuit to another AFCI circuit; fault follows circuit not circuit * switch back to AFCI, open up boxes between last outlet and breaker and test with a test outlet off each box/junction I can find; can't make it trip; I did reuse the wire nuts; Fixed!) many many months go by * trips under load again * get another AFCI breaker (15 instead of 20A; yes I downsized even though it was tripping -- I didn't think it was tripping from load and I wanted some buffer against the potential there were 14ga wires in the branch) and a bag of wago connectors (for another project). Replaced the breaker -- still randomly tripped but wasn't surprised. (I found an electric supply place only 20 minutes drive away that had the correct siemens breaker style, and finally had free time when they were open!) * open up boxes (again) and replace wire nuts with left-over wago connectors from prior project. That fixed the problem. Now -- the flaky junction was in a steel junction box, but that box was nailed into a rafter against the ceiling. Could it have caught fire? Maybe? It was a 20A circuit, with 12gauge wire. I'll say yeah, it could have started at least smoking if it'd been on a dumb breaker.