When you turn on a unit that has an oscillating draw on power, it will cause the voltage to jump up and down as the alternator won't be er to adjust to anything greater than whatever power it can push out. The more demand you put on the system, the lower the total power availability will be shown on the volt meter. The needles on the gauges always fade from daylight exposure. Go to a hobby shop and buy some signal orange paint and a fine brush to touch them up. If you haven't swapped the backlights and warning light globes for LED's yet, get onto ebay and buy some in bulk packs of T10 wedges (I've bought a couple of packs of 10 for $0.99 each). They really lift the instrument cluster lighting