Add ham slices, pineapple slices, and maraschino cherries to the slow cooker.
Whisk the reserved pineapple juice, brown sugar, mustard, and apple cider vinegar in a medium sized bowl until smooth.
Pour the suace over ham, pineapple, and cherries in the slow cooker.
Cover, and cook for 5 hours on LOW, with out opening the lid during cooking time.
Drizzle sauce over each serving. ENJOY!
