If the starter clicks but won't crank, try turning on the headlights.
If they are dim, and go out when cranking, yup, battery...
If they remain bright when click, then it's the starter...

SOMETIMES a bad starter can cause the lights to dim, when the windings are damaged...

Also, a starter that repeatedly clicks is a weak battery...

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!