Well, over the years I've learned that bad grounds can cause all kinds of weird stuff. I'd just try splicing in a good ground to the existing ground wire and see if that makes a difference. What about the other wire(s)? There could be a break/bad connection there too. BTW - Twist splices and electrical tape are not a repair. If you don't have a soldering iron, get one. Also pick up a wire stripper, some silver solder, soldering flux, some heat-shrink and do proper repairs. About the only repair I'll make w/out soldering is to use a butt connector and I don't trust those kinds of repairs either. That's a real rat's nest of wires you've got there.