flashing lights
 

I have a pulse in all my lights. The headlights, dash lights and lights in the radio all have a pulse. I had the battery tested and it turned out good. I also had the alternator tested, good also. I'm thinking its a ground somewhere. When Im driving all my lights flash and the battery gauge with bounce from 14 to 16 volts back and forth. I have a 99 trailblazer by the way. Can anyone give me any advice on how to fix this??