You will get a dozen different ideas so here's mine . I use Detail Tack from Micro Mark , probably the same as Tacky Glue at Michael's . A small dab using a toothpick on your painted surface , let it dry , then place the light or mirror in place . . . done . Some will worry about it drying out over time but I have models on my shelf 10 years old and the mirrors are still there . If you are concerned apply Tacky Glue to both surfaces , it works like contact cement and will create a very strong bond but can still be carefully removed if needed . This bottle is 10 years old , it lasts a loooong time .