#1
A wire came off my input jack. A buddy resoldered it and my guitar was fine. THan two days later the volume and oomph would drop from my guitar. It still plays though. Toggling jack and pickup switches makes no difference. The solder is still in place. Should I resolder? replace the jack?
#2
re-solder , it's probably a cold solder joint or maybe the wire isn't in enough. if anything. People would be surprised how many times I've legitimately switched an input jack even on guitars I've re-wired 5-10 times minimum due to my tone chasing

one other common mistake I see is sometimes guys when they fix wiring in a guitar or put in a new harness at times they put the pots in again and position them where the contacts you solder to are touching to the walls of the guitars control cavity. 9 out of 10 there is shielding or paint on there to reduce hum. So this is something to look for.

look at anything that was re-soldered , cold solder joints are dull looking instead of shiny just melted solder. Cold solder happens because of dirty soldering iron tips. So a wet sponge and or cleaning the burnt on wires and all with say copper looking steel wool similar to what you wash dishes with come in handy.

When I was re-wiring a personal guitar I had the same issue and it was the hot lead giving me the issues. My case it was a rushed job of me excited to try out a new concept. But of course let's see what others have to say.