1998 Dodge Neon Totally quit

Daughter driving car at 25-30 mph and the vehicle totally shut down. She was able to put it in neutral and coast to side of road. With the exception of some aftermarket fog lights installed by previous owner, there is NO electrical activity. No lights, no radio, no cranking, etc. It behaves as if there were no battery. I replaced a fuse that was suspicious (40 amp ignition) and also an "auto shutdown relay" which is located in the fuse box. Neither fixed the problem.