Place the eggs into a saucepan in a single layer and fill with water to cover the eggs by 1 inch. Cover the saucepan and bring the water to a boil over high heat. Once the water is boiling, remove from the heat and let the eggs stand in the hot water for 15 minutes. Pour out the hot water, then cool the eggs under cold running water in the sink; peel and chop the cooled eggs.

Bring a large pot of salted water to a boil. Add potatoes and cook until tender but still firm, about 15 minutes. Drain and set in the refrigerator to cool.

Fill a large pot with lightly salted water and bring to a rolling boil over high heat. Once the water is boiling, stir in the macaroni, and return to a boil. Cook the pasta uncovered, stirring occasionally, until the pasta has cooked through, but is still firm to the bite, about 8 minutes. Drain in a colander set in the sink; rinse with cold water.

Whisk together the mayonnaise, vinegar, curry powder, celery seed, salt, and pepper in a bowl. Combine the cooled potatoes, macaroni, chopped eggs, carrots, peas, and onion in a large bowl. Carefully stir in the dressing; cover and refrigerate overnight.