Search for the terms 545T. Its a device made by DEI/VIPER and is now cheap. That will help you add auto-on headlights. Several threads on that device on this forum and a DIY too. Please ask additional questions in one of those existing threads.
I just ordered this part from Amazon for just under $30 and prime shipping - FYI.
Will look at directions and see how it goes in. Not sure from suggested thread and description if it comes with the light sensor or how that all works. Used to GM cars and this thing is dumb to not have something that costs so little to add to the vehicle on the assembly line!