Starter motor or solenoid worn or poor connections to the srarter. Man. or auto. trans? And while we are at it what engine? Cause i just wan't to know! Start with the neg. cable, clean & tight both ends? Now pos cable tight & clean at batt. and solenoid? Now on the other side of solenoid is cable tight & clean? Now at the starter same thing. Now the little wire at starter same thing? If all that is ok it is either fender mounted solenoid or bad starter.
Ok now with trans. in park at the fender mounted solenoid see the two big cables? With a pair of plires(metal handles) touch each of these termanils( will get sparks) but see if starter will turn. if so the solenoid is bad! If not starter or cable is bad. This is if battery is at full charge and cables are clean and tight!