i have an 02 camaro z28 ls1,on occasion the car wont start,you turn the key and everything comes on even the click for the fuel pump,the gages read 12-13v but the car wont crank.its been to the dealer and nobody can figure it out.the only way to start it is a jump start and sometimes this wont work either,also there is a rear window defroster problem it will only stay on for about a minute and wont turn back on.
Check your positive connections and then check the ground.
Remember to check both ends of each battery cable. Remove and clean each end. It is possible for a cable to fail internally so you can’t see it.
It also could be a a starter or relay problem.