if you are having trouble starting the car, and jumping sometimes works, you more than likely have loose belts on the alternator, and or are having alternator problems. I would pull the battery out and have someone take it to autozoo or somesuch and fully test the battery. and fully charge it if it's weak, but good. replace it with a solid group 49 if it's bad.

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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!