here is the story I started my car it crank slow put started. then I started driving. as I was driving I notice the cars voltage gauge on the dash go way down. I turned the head light off and it help alittle with it going back up but it was still low. I parked the car. later I tryed to start the car and now it just clicks rapped. it will not even turn over or try to start just tick tick tick I have a brand new battery. my battery cables are tight and free of rust. I tried puting a new alternator in the car and that was not the right thing to do. I can't keep throwing part at this car. need help fast

 

Hmm.. My car did this last week. It was a very rapid clicking sound coming from the engine. But I fixed it by getting a new battery.. How new is this battery? Are you running subs and lights etc. ?
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edit - also check the wires between the battery, alternator, and starter. Tap the starter lightly with a hammer and see if turns over. If it does, it means your starter's probably going. I also read that there's a fuse for the electric fan that can prevent the alternator from charging.

 

my battery is only 1 week old. I looked at the battery connections they look all good and tight. but no start or crank