either your jackplate or shielding is keeping the ground to the sleeve or middle lug with the wire broke off. that sleeve needs to be grounded, so that when you put a plug in, it grounds the sleeve AND the negative battery wire(ring) together. its what switches the battery on and off, and is a SOLID ground for the jack vs trusting the shielding or jackplate. it works, as you can see, but i get it soldered back up.
does the blue wire on the effects jack that the broken wire went to have another blue wire running to another ground? or is that the wire running to the control plate?
Disclaimer: I make and sell Buffers. I also sometimes Modify, Build and sell preamps and amplifiers. My opinions are not intended to be sales pitches. I am a one man shop and prefer to spend time with my wife and family, i work full time on call and love to spend my spare time doing other things. I only make, modify or build things for those that seek them.