1999 Dodge Caravan intermittent electrical problem

This problem occurs usually at night when all of the lights and accesories are on. All of the lights will flash off for approximately 1/2 second and at the same time the guages will all go to zero and stay that way for 2-3 seconds, then they will return to normal accompanied by the tone that chimes when you first turn on the key. It will sometimes happen 3-4 times in a day and other times will be more than a week apart. I have checked the relays, fuses and fuse holders and all appear to be OK. I thought that it possibly could be the ignition switch being as it does have a considerable amount of wear but I don't see how that would affect the lights. Does anyone know what this problem could be?