So in my 84 z28, I've had a persistent electical issue where the volt gauge would shoot way up to its max and stay there for long periods of time. The alternator was replaced about a year ago and it didn't really fix it. The car does have an amp and 2 subs in it, could that be messing something up? There is also a short somewhere for when you turn the headlights on the tach gets stuck where it is and the oil gauge bottoms out. Could the short be causing an issue with the rest of the system?

 

That sounds too complex to give advice w/o hands-on, but it sounds like someone hacked into the wrong wires.. (Both the oil gauge & the low beams have tan wires for instance.) Anything could have been done here & I can't think of what the issues might be. Very strange..