How old is the battery? A fading battery will cause a lot of odd problems. Hot summers are killers for batteries and if you don't drive your car much (e.g.--weekend toy) then the battery should be the prime suspect.
Does the car start OK? Do the gauges sweep during cranking? The sweep is a pretty good indication that the battery is week.
Where to find the problem: Using a good magnifying glass or loupe, look at the pin ends that come through the board and look for the cold joint (as per the article). You will see a break or crack in the solder and that is causing the bad connection.
Where to find the problem: Using a good magnifying glass or loupe, look at the pin ends that come through the board and look for the cold joint (as per the article). You will see a break or crack in the solder and that is causing the bad connection.