1998 Dodge Truck Wont start

Are you saying the starter motor won't even crank? The starter relay shows to be located in the power distribution center, under the hood. With the key in the crank position, what is the reading across the battery posts?. If the reading is still 12.3v, you have an open circuit. In the diagram terminal 30 is hot all the time. Terminal 86 is voltage for the coil side of relay, goes hot with the key in the crank position. Terminal 85 is ground for the coil side of relay and is grounded through the neutral switch. When the relay is energized, terminal 87 goes hot and carries to starter solenoid. Any testing at the relay make sure the tranny is in park or neutral and the e-brake is set.