Do truck manufacturers use standardized wiring harnesses regardless of the model?

Do they use the same harnesses whether it is a baseline model or a fully loaded model and just not put on the additional parts?

For instance if the model you bought did not have a backup camera but that is an option on other models and you wanted to come back and add one later could you do so by adding the camera and screen without needing to add all the wiring from front to back?