If you want, you can throw parts at it until you are blue in the face. It's your wallet. However, if you would like to really find out quickly what is wrong with it you will need a multimeter. With the leads placed across the battery, and taking readings in Vdc and Vac, with the engine running, you can almost immediately determine what is wrong. Anything else and your just guessing.

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Sam

84 300SD 350K+ miles ( Blue Belle )