1998 jeep Cherokee limited 6 cylinder will not start at all. Turn the key and get nothing.Full power to headlights and radio. Starter has been checked and tested good. battery tested and is good. Tested all fuses. Also notice that the backup lights have not been working for several months despite new bulbs being inserted. Before the jeep quit working it has been slow to start on many occasions and sounded like the battery was drained when cranking but it was not drained. Any suggestions?