I am replacing a alternator on a Mercury mystique 98 any suggestions?

They are going to charge you a king's ransom for that alternator. So I suggest finding a shop in your town that specialises in rebuilding alternators/starters. You will end up paying a quarter to a third of what you'd spend on a new one from mercury and maybe half of what you'd spend on one from the local parts store. P.S don't believe anyone who trys to say rebuilt ones suck. They come with a warranty too. Make sure to clean up all the cable contacts and replace any corroded wiring.