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There are a few things that could be causing it. 1. the battery. 2. The starter 3. The starter relay. 4. The starter cables themselves. With electrical parts I 100% advise
against junk yard parts. Sitting around rusting is worse for electronics than being used constantly. What you are describing sounds like the battery. It could also be the cables or corrosion preventing the power in the battery from reaching the starter. It is also possible the starter has developed so much resistance that it is causing this problem, but usually a drive pinion breaks or they simply stop functioning before that point.
If you can take a known good battery from a friend's car and try it in yours. If it still doesn't work. I'd check the condition of your cables. They are 21 years old. You may also find more specific help here, from people more experienced in that specific car.
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