Intermitant start



1996 Nissan Sentra GXE 1.6ltr. Drive to park. walk dog. return to a car that macks to sound while attemting to start. removed key from ignition and cluster lights are still on.2007 Battery was load tested and said to be battery did not help. Starter was replaced as mechanic says power to starter was ok. Drive home from shop. Car will not start net morning. I have replaced the alternator a few years ago. Battery terminals have been upgradded. 1/2 later after doing nothing the car starts and I drive 2 blocks to shop. Shop starts car about 17 times and says everything is OK. I think I need a new ignition switch, or I have loose wires that I can check by starting the car in the dark while wiggling wires under the hood and looking for sparks. Or is the alt. bad again.