From Sheldon Simeon's "Cook Real Hawaii" book. Yes, that is 3 cups of mayo. Trust me, it seems like too much but its the right amount.
Peel the potato and chop into 1/2 inch cubes
Roughly chop the hard boiled eggs
Grate the carrot using a cheese grater
Boil the macaroni in a pot of salted water for a few minutes longer than the directions say. You don't want it to be al dente, you want it to be just a bit mushy. Chill it in the fridge
Change out the water for some new salted water and boil the potatos until soft, about 10 minutes
Mix together the eggs, mayo, garlic salt, pepper, and carrots to form a smooth mixture, then fold in the potatoes and macaroni.
Ideally let this whole concoction chill in the fridge for at least 30 minutes to allow everything to meld together before serving