Do the needles on your gauges jump around, sweep from side to side or just plain refuse to budge? How about your other electrical accessories—do they work intermittently or so strangely that you swear they’re possessed? If so, it’s time to clean your ground cables.
The pros always start by cleaning the ground cables. Carmakers use the steel body as the return “ground” electrical path, so when the cables corrode (and they will corrode), the stray current can cause all sorts of strange behavior.
A rotary tool with a wire brush works great. But you can also use sandpaper. The key is to get shiny metal on all the connections. Use a shop manual to find the locations of the other ground connections in your vehicle.