Soak the beans overnight. Place the beans in the insert of a slow cooker and cover with water by about 3-inches. Let sit at room temperature overnight. Don't turn on the slow cooker. Drain the water in the morning and add fresh water to cover the beans by 2-inches.
Add the ham bone, tomato sauce, onion, chile, garlic, chili powder, salt and pepper and cook on low all day, 6 to 8 hours, until the beans are tender.
Toward the end of the cooking time, you can remove the meat from the ham bone and add it to the beans, but the beans will be delightfully flavorful without it too. Taste the beans to see if they need more salt and pepper.
Notes
Regarding the guajillo chile, look for it near the Mexican spices in the latin section of your market. It's a smoky chile, but it's not hot. Other chiles may be substituted: suggest pasilla, ancho or New Mexico chile.