On my Mossberg 500 I put a rear pistol grip on with a side saddle shell holder.
In the rear most slot of the shell holder I put a sure fire flashlight mount that fits in one of the shell slots.
The flashlight had a push-on, let go-off button on the rear of the light that I could use with my thumb while still gripping the rear pistol grip.
This was the perfect set up and it worked well for me.
It can allow you to light up the night and let go to adjust your position while the bad guys are temporarily blinded as a fixed "on" light can be deadly if the bad guys are shooting at the direction of your light.
I snuck up on a pack of wild dogs that were terrorizing my shepherd out back one night.
The flashlight worked just as I planned and got their attention as I moved to another spot and opened fire.
The biggest regret I had was putting a front pistol grip on this pump shotgun.
Don't do it....it is so uncomfortable and takes away from the stable feel of the gun and just does not feel right......it's more of a hindrance in my opinion.
The pic below is very similar to what I had but my light was in the rear slot with a push button at the rear of the flashlight.
The coil cord and pressure switch is okay and I tried that but did not like the bulk of the cord because I did not want the extra obstruction near my spare shells.
I had since sold my shotgun to someone that really begged me for it so I need to build another one.