Voltage issue

if hit a bump made difference, definitely a connection failure somewhere. Could be in the positive/actual wire and terminal side of the circuit. Could be in the ground/nut and screw side too. The voltage regulator needs a good connection to chassis ground. if the factorys nut and screw method doesn't work, adding an actual wire for the ground path will.
As for the madelectrical link... Where would you be today without your ALT' gauge ? Don't cut out your gauge unless you'll replace it with some other indicator.