This Mac Salad is from the gorgeous Aloha Kitchen, a cookbook by Alana Kysar about Recipes from Hawai'.
Cook the macaroni, salting the water with 2 Tbsp kosher salt, according to instructions on package until tender. Drain, transfer to a large bowl, and set aside for 10 minutes to let cool.
Once cooled, fold in onions, 1/2 cup mayonnaise, pickle relish, pickle juice, and a dash of pepper and toss until well coated. Taste and season with salt and pepper.
When ready to serve, stir in 1/2 cup mayonnaise and the shredded carrot. Taste and add more mayonnaise if it looks dry or more salt if it needs it. Serve chilled.