I have three exterior lights, which are controlled by one switch inside. I would like to add a motion sensor to control all three lights. I don’t want to use the inside switch anymore. Is it possible to add the motion sensor and if so where should it be added. Could someone please give me detailed information (which wire or before or after which light), as I am not very experienced? I have replaced light fixtures in the past but I don’t know much about multiple lights on one circuit or adding switches or sensors. Thank you very much.

You can wire Motion Floods at each location, black to black and white to white pluss all grounds.
You will know where the activity is by which lights activate.
Another way if you can get another wire between each lights, then they can connect to the switched leg from motion(usually a red wire) to each other, then if motion is detected from any of the 3 motions, all lights will light.
Do not exceed the Maximum wattage of ONE fixture, with the Total of all bulbs.

Originally I installed a sensor light (the ones with the two floodlights) on each location but this did not work out very well. I am guessing it exceeded the maximum wattage. So I re-installed the 'normal' outdoor lights.

All of the lights are on one side of the house and one sensor in the middle would pick up motion on the entire area. I would only need one sensor. Could I just add a sensor somewhere in the circuit to turn on all the lights?

Thanks for your help.

You don't have to guess, add up the bulbs and check maximum. The third wire controls the lights.