I added a six shell side saddle to mine and used one of the shot holder holes in the side saddle to mount a sure fire flashlight with a special mount that fits in said shot shell hole.
The light has a rubber push button at the very rear that you can just push on, let go, off in place of. A remote switch.
My gun has a rear pistol grip so I just pivot my thumb up to press the light button as needed.
When I let go, the light is off.
This worked very well for me especially while sneeking up and blasting a pack of wild dogs that was terrorizing my Belgian Malinois Shepherd one night out back.
I Surprised them with the instant on light and was able to fire a few shots all while holding the light button with my thumb and racking the next shell.
I was able to kill two out of three of the bad dogs, amd when I say bad they were bad because they tore the neighbors jack Russell to bits the previous night.
I had since sold this shotgun but I can try to find a pic of my simple but very functional set up.