The terminal on rear of my chrome alternator where the main wire hooks up was loose and sparking. Is there supposed to be a plastic piece on the terminal to keep it from contacting the alternator case?

Is there supposed to be a plastic piece on the terminal to keep it from contacting the alternator case?
It should be on the alternator. It may be pushed in to deep.

Yes, there should be an insulator type of washer there to prevent the Alternator wire from grounding to to body. I believe they sell the washer in a kit along with the rubber boot.

Thanks for the help, I'll get a piece in there.