how do i fix electrical issues and where are the grounds located

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Im having an electrical issue where when I start the car, the rear window wiper blades run, when I use the left blinker, the blinker and the security light comes on, and when I use the right blinker the hazards come on. Also, when I pop the hood, the horn goes off until i disconnect the battery. and the positive cable will not tighten on the battery anymore. I also had an issue today where the check engine light and the TCS and slippery road warnings came on. Once I disconnected the battery and reconnected, those disappear. What are my options and how much will this cost to fix.